What does "100% crop" mean? (Noob question)

I've been a member here for a while, and just recently bought my first DSLR (450D, previously owned an S3 IS). When people post pics, I often see them mention that it's a 100% crop. Not to sound totally ignorant, but what does that mean?

"100% crop" is a crop area of an image viewed at 100%
The cropped image, then, should not be resampled to be considered 100% crop. The term may be used incorrectly to describe an uncropped/full-frame image.

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Most programs automatically size images to fit on your screen. A 100% crop is a crop of the image if viewed at the actual pixel size.

It's usually used to determine if an image is sharp or if focus was accurate.

Thanks for the replies. I actually found another old thread here on the same subject but you both explained it in a much clearer and briefer fashion.

gregrocco wrote in post #6113664
Thanks for the replies. I actually found another old thread here on the same subject but you both explained it in a much clearer and briefer fashion.

I still don't understand.

Do this.

Open up a photo in Photoshop. In the upper left corner it will show the full picture and probably '25%'. Change that to 100% and you will you are REALLY zoomed in. That is the 'real' size of the image. Crop out what you see in your viewing window. Save and now you have your crop!

I actually understand now.... THANKS!!!

Edit.

Upper right hand corner you will change to 100%

I always found it easier to use a marquee tool to carve out a specific number of pixels, usualy 1,000x1,000 and post without resizing.

Thanks guys...

These are 100 percent crops from a my new 24-70L. I think I have it figured out.