What does ISO stand for on digital SLR cameras?

ISO is the number indicating a digital camera sensors sensitivity to light. The higher the sensitivity, the less light is needed to make an exposure.

in manual SLR, ISO is the film speed for capturing the light.. but in digital SLR (since there's no film), it determines the sensitivity of the sensor to the light..

higher number of ISO means the sensor is more sensitive to the light, this means with low-light situation you can still able to capture your object.. for example in the under-lighted interior rooms or even in the night shot.. I usually use ISO 400, 1000, 1600, even 3200 for taking picture in the dark.. but remember that the quality of the pics won't be as nice as those lower ISO (from 50 until 200).. lower ISO usually used on bright and sunny condition

Hope this helps

I think ISO stands for "International Standards Organization" or the foreign languare equivalent. But here's a page to give you a visual representation of what it means.

http://www.photonhead.com/beginners/film...

If you put "ISO ASA" into a search, you will get several more examples and explanations.