A plain-English photography glossary.

Ambient light to color space, A through C.

The first stretch covers light you did not put there, the openings and shapes that control it, and the words for what happens behind you.

• Ambient light. The light already in a room before anyone adds anything. Indoors it usually comes from overhead fittings, which is rarely kind to a face.
• Aperture. The adjustable opening inside a lens, written as an f-number. A wide aperture such as f/2 lets in more light and keeps less of the scene sharp; a narrow one such as f/11 does the opposite.
• Aspect ratio. The shape of an image, written as width against height: 1:1 is square, 4:5 upright, 16:9 wide. Changing the ratio always means cutting something away.
• Backdrop. The surface behind you in a studio, usually paper or fabric in a plain color. Its only job is to keep attention on your face, which is why the good ones are dull to look at.
• Bokeh. The character of the out-of-focus areas in a picture, not merely the fact that they are blurred. Smooth, round bokeh recedes politely; harsh bokeh has hard edges that pull the eye off your face.
• Broad light. Lighting in which the side of your face turned toward the camera is the lit side. It widens a face, which is occasionally what you want.
• Catchlight. The small reflection of the light source visible in the eye. It is what makes eyes look alive, and its absence is why a technically correct portrait can still feel dead.
• Color space. The defined range of colors a file is meant to be read in, such as sRGB for screens. A file opened in the wrong space shows the wrong colors, which is covered in the difference between sRGB and CMYK.

Depth of field to gamut, D through G.

These are the words for sharpness, for softening light, and for the reason a print and a screen never quite agree.

• Depth of field. How much of the picture, from front to back, is acceptably sharp. Shallow depth of field lets the background fall away and keeps attention on the eyes.
• Diffusion. Any material that spreads light across a wider area, such as fabric stretched in front of a lamp. It makes the source effectively larger, which softens the edge of every shadow.
• DPI. Dots per inch, a printing measure of how densely ink is laid onto paper. 300 dpi is the long-standing convention for photographic printing.
• Exposure. How much light reaches the sensor, set by aperture and shutter speed, with ISO deciding how bright an image is made from it. Correct exposure means the tones you care about, which in a portrait means skin, land where you want them.
• Fill light. A softer secondary light that lifts the shadow side of a face so it keeps detail. It is not there to remove the shadow, only to decide how deep it goes.
• Focal length. The lens measurement in millimeters that decides how wide or narrow the view is. Longer focal lengths let the camera stand further back, which keeps a face in its own proportions.
• Gamut. The range of colors a device can actually produce. A screen's gamut and a printing press's gamut do not match, which is the root of most print disappointments.

Hard light to modifier, H through M.

The middle of the alphabet holds most of the lighting vocabulary, which is the part of a session worth having an opinion about.

• Hard light. Light from a small source, giving sharp-edged shadows and bright highlights. Dramatic, and unforgiving of skin texture.
• High key. A deliberately bright, low-contrast look on a light background with shallow shadows. Clean and current, and a common choice for corporate portraits.
• ISO. The sensitivity setting of the sensor. Raising it lets you work in less light, at the cost of more noise in the image.
• JPEG. The common finished image format, opened by everything and compressed to keep the file small. Every time one is edited and saved again it gives up a little quality.
• Kelvin. The scale used to describe the color of light, running from warm orange at low numbers to cool blue at high ones. It is what white balance gets set against.
• Key light. The main light on your face, the one deciding the direction and shape of the shadows. Every other light in the room is described by its relationship to this one.
• Low key. A darker, higher-contrast look on a dark background, where the shadow is doing most of the work. The named looks are compared in studio lighting styles explained.
• Megapixel. A unit describing how many pixels a camera records. It decides how large you can print, and it is a poor measure of how good a photograph is.
• Modifier. Anything placed in front of a light to change its size, softness or direction: a softbox, an umbrella, a reflector, a grid.

Natural light to rim light, N through R.

This stretch covers the light nobody controls, the format your photographs begin life in, and the work done after the sitting.

• Natural light. Daylight, usually through a window. Large and soft under an overcast sky, small and hard in direct sun, and never the same twice, which is the whole argument in natural light against studio light.
• Noise. The speckled texture that appears when a sensor is pushed in low light. Software reduces it, though heavy reduction takes skin texture away along with it.
• Prime lens. A lens with one fixed focal length and no zoom. Usually sharper and better in low light, and it makes the photographer move rather than the lens.
• RAW. The camera's unprocessed capture, much closer to an exposed negative than to a photograph. It holds the sensor's data with no decisions applied and has to be developed before anybody sees it.
• Reflector. A pale panel used to bounce light back into the shadow side of a face. The simplest way to soften a shadow without introducing a second light.
• Resolution. The pixel dimensions of an image, which decide how large it can be reproduced before it goes soft. How much you need for a given job is settled in how much resolution you need.
• Retouching. The finishing work on a delivered photograph, done by hand: color, tone and small corrections made so the picture still looks like you.
• Rim light. A light set behind and to one side, drawing a bright edge along hair or shoulder so you separate cleanly from the background.

Short light to working distance, S through Z.

The last stretch is the vocabulary of the studio itself, plus the two terms that decide most of what a portrait looks like.

• Short light. Lighting in which the side of the face turned away from the camera is the lit side. It narrows a face and is the more common choice in portraiture.
• Softbox. An enclosure that turns a small light into a large, even one. The bigger the box relative to you, the softer the shadows.
• sRGB. The standard color space for screens and the web. Save a web image in anything else and browsers may show its colors incorrectly.
• Strobe. A studio flash firing a short burst of light. It freezes movement and overpowers the room's own light, which is what makes a studio result repeatable from one frame to the next.
• Tethering. Connecting a camera to a computer so the frames appear on a larger screen as they are made. Some photographers work this way and some do not, so it is a working preference rather than a standard to expect.
• White balance. The setting that tells the camera what color the light is, so that white things come out white. Wrong white balance is why skin sometimes goes orange or faintly blue.
• Working distance. How far the camera stands from you while it works. It is the quiet decision behind whether a face keeps its own proportions.

The words people mix up.

A handful of these get used loosely, including by photographers, and the confusion causes real problems at the point where somebody has to send a file or approve a picture.

• DPI is not resolution. Resolution is how many pixels an image has; dpi is how densely they get printed. The same image can be printed small and dense or large and coarse.
• Bokeh is not blur. Blur is the fact of being out of focus. Bokeh is the quality of that blur, which is why two lenses can blur a background by the same amount and still look completely different.
• A filter is not retouching. A filter applies one rule to the whole picture. Retouching by hand means a person deciding, area by area, what to leave alone.
• Megapixels are not quality. They set the largest useful print size and nothing else. Light, lens and direction decide whether a picture is any good.
• RAW does not mean unedited in the sense of honest. It means undeveloped, and it looks flat and dull because no decisions have been made yet.
• Natural light does not mean outside. It means daylight as the source, and the best of it is usually indoors, beside a large window, out of direct sun.

If you are choosing a photographer and want to test whether the vocabulary is being used to inform you or to impress you, how to choose a photographer gives you better questions to ask than any of these words.