Here at photomacrography.net, the phrases "100% crop" and "actual pixels crop" mean an image that is equivalent to duplicating your original image, cropping without resizing to an area that is 1024 pixels square or smaller, saving that small cropped version to a JPEG with file length < 300KB, and posting the result.
The reason we emphasize "without resizing" is because it's possible (for example) to use the Photoshop crop tool with options set so that it does resize, silently and implicitly. The results of that process can lead to some pretty confused discussion.
The reason we emphasize "1024 pixels square or smaller" is that the forum software will automatically resize images to be maximum 1024 pixels dimension, if the file being uploaded contains a larger image than that. To avoid resizing, the source image must be 1024 pixels or smaller.
In Photoshop, a safe way to do cropping without resizing is to use the rectangular marquee tool to select the area you want, then use Image > Crop.
Note that in other communities, the phrase "100% crop" might mean something completely different: the entire frame, 100% of it, resized as required for posting. You can think of the distinction as a matter of local dialect.
Here are summaries and links to discussions for Frequently Asked Questions.
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