at the risk of sounding silly

[rossco]

what does 100% crop mean

[hoffy]

I think 100% crop is a silly term. By true definition, if you cropped a photo to 100%, you are not cropping anything at all! If you cropped off 100%, there would be no photo to see....

OK, now that I have the smart arse comment out of the way, they are referring to opening a picture, displaying the actual full size of the picture and cropping a small section out of it, so the small section can be displayed as the full size. Generally used to pixel peep

[rossco]

ahhhhh, thank you sir hoffy

[ricktas]

Yep, zoom in to 100%, and then crop as Hoffy says. Often used to pixel peep. Look at noise, chromatic Abberation (CA), sharpness etc at the pixel level.