One of the things I always mention to my clients is that some cropping may occur when they print from digital files. Unless the original digital image is cropped by your photographer or by you to fit a specific print size, digital files are not be formatted to "fit" any standard print size. Here is why:
One of the properties of a digital image is its dimension in pixels - length and width. My camera is an 18-megapixel camera and records digital files that are 5184 pixels long and 3456 pixels wide. Its ratio of length to width is 3:2, which means that digital files will make 3 by 2; 6 by 4; 12 by 8, 24 by 16 prints without cropping (in other words, there will be no cropping as long as the original ratio is preserved). Every camera is different in regards to the length-width ratio of the images it records, there is no set standard.
The image below has a 3:2 length to width ratio. There will be no cropping as long as this image is used for a 4*6, 8*12 and so on print.

Now, let's see what happens if we use this digital file to make a 5 by 7 print. White lines in the image below represent how the original image will be cropped. The "long" side of the resulting print will be slightly cropped.

Cropping will be even more substantial if we choose to make an 8*10 (or a 16*20) print:

I usually recommend that if my clients receive digital files from me, they should check how their images will be cropped before printing. Most online and in-store printers give "previews" of how a printed image will look and have tools that allow customers to recompose their images for printing.
As a photographer, I usually compose my shots with a little extra "space" on all sides so that no important part of the image is lost later due to cropping for print.