To start with here are the definitions:
Crop
When you crop an image, you trim away material from the edges to show a smaller area, often for artistic reasons.
Print dimensions, resolution, and resizing
Resolution is the size digital image pixels print as dots, and represents the amount of detail in an image. It is measured in DPI (Dots Per Inch). Printing requires a higher resolution than viewing a photo on a computer monitor. For more information, see:
Resizing means to change the print dimensions (the length and width in inches or other scale of measure) of a photo.
To resample means to change the pixel dimensions of an image (by either adding or removing the total number of pixels). You resample primarily for onscreen viewing. Resampling always reduces image quality. Resampling to smaller dimensions reduces file size and sharpens appearance. Resampling to larger dimensions increases file size and blurs appearance.
