What does it mean?

ISO

"In traditional (film) photography ISO (or ASA) was the indication of how sensitive a film was to light. It was measured in numbers (you’ve probably seen them on films – 100, 200, 400, 800 etc). The lower the number the lower the sensitivity of the film and the finer the grain in the shots you’re taking.

In Digital Photography ISO measures the sensitivity of the image sensor. The same principles apply as in film photography – the lower the number the less sensitive your camera is to light and the finer the grain. Higher ISO settings are generally used in darker situations to get faster shutter speeds (for example an indoor sports event when you want to freeze the action in lower light) – however the cost is noisier shots. I’ll illustrate this below with two elargements of shots that I just took – the one on the left is taken at 100 ISO and the one of the right at 3200 ISO (click to enlarge to see the full effect)."

http://digital-photography-school.com/iso-settings

F Stop/ Aperture

"Put most simply – Aperture is ‘the size of the opening in the lens when a picture is taken.’

When you hit the shutter release button of your camera a hole opens up that allows your cameras image sensor to catch a glimpse of the scene you’re wanting to capture. The aperture that you set impacts the size of that hole. The larger the hole the more light that gets in – the smaller the hole the less light.

Aperture is measured in ‘f-stops’. You’ll often see them referred to here at Digital Photography School as f/number – for example f/2.8, f/4, f/5.6,f/8,f/22 etc. Moving from one f-stop to the next doubles or halves the size of the amount of opening in your lens (and the amount of light getting through). Keep in mind that a change in shutter speed from one stop to the next doubles or halves the amount of light that gets in also – this means if you increase one and decrease the other you let the same amount of light in – very handy to keep in mind)."

http://digital-photography-school.com/aperture

Exposure

"Exposure is the amount of light collected by the sensor in your camera during a single picture.  If the shot is exposed too long the photograph will be washed out.  If the shot is exposed too short the photograph will appear too dark.  Almost all cameras today have light meters which measure the light in the given shot and set an ideal exposure automatically."

http://www.picturecorrect.com/tips/photography-exposure-basics/

Depth of Field

"The definition of Depth of Field (DOF) is the distance in front of and beyond the subject that appears to be in focus.

What does that mean exactly?
It's commonly misunderstood that the out of focus or blurry part of the photo is the Depth of Field. In truth, the in-focus or sharp part of the photograph is the Depth of Field. Having a larger field of depth means more is in focus while having a smaller field of depth means less is in focus. The depth of field is completely controllable using your lens, focus, and aperture."

http://photography.nuvvo.com/lesson/30-photography-depth-of-field

White Balance 

"White balance (WB) is the process of removing unrealistic color casts, so that objects which appear white in person are rendered white in your photo. Proper camera white balance has to take into account the "color temperature" of a light source, which refers to the relative warmth or coolness of white light. Our eyes are very good at judging what is white under different light sources, but digital cameras often have great difficulty with auto white balance (AWB) — and can create unsightly blue, orange, or even green color casts. Understanding digital white balance can help you avoid these color casts, thereby improving your photos under a wider range of lighting conditions."

http://www.cambridgeincolour.com/tutorials/white-balance.htm

Shutter Speed

"Shutter speed is the amount of time that the shutter is open.

In film photography it was the length of time that the film was exposed to the scene you’re photographing and similarly in digital photography shutter speed is the length of time that your image sensor ‘sees’ the scene you’re attempting to capture."

http://digital-photography-school.com/shutter-speed