Adobe Encapsulated PostScript files are files which are intended to be encapsulated (or incorporated) into other Adobe PostScript files. They are subroutines which are called by copying them into the proper location within the larger Adobe PostScript file.
Because EPS files are intended to be part of a single page, they must be single page images themselves.
Because they are usually processed by encapsulating programs which do not have language level knowledge of the EPS file’s contents, they should include Adobe PostScript Document Structuring Comments (DSC) and conform to constraints so that the encapsulating program can obtain its desired results.
A proper EPS file when it has been executed should leave the interpreter, except for any image generation, in the same state as the interpreter was in when the EPS file received control. A proper EPS file should honor any translation, rescaling or rotation established by the encapsulating code. A proper EPS file should not use any commands which reset the interpreter’s state or cause an image to be displayed.
EPS and its requirements on a PostScript file are described in considerable detail in Appendix H of the second edition of the PostScript language reference manual, a.k.a. the Red and White Book.