zip is a command line utility for linux,unix,VMS, MSDOS,OS/2, Windows 9x/NT/XP, Minix, Atari,Macintosh, Amiga, and Acorn RISC OS which is used to archive/compressed a set of files,folder. It  is analogous to a combination of the Unix commands tar(1) and compress(1) and is compatible with PKZIP (Phil  Katz’s  ZIP  for  MSDOS  systems).

ZIP command compressed the set of files and unzip UN-compressed.

USE

aon@ox-Vostro-1550:~$ zip -r foo.zip foo
[Note: foo is a directory and archive name is foo.zip]
To UN-compressed foo.zip run bellow command

aon@ox-Vostro-1550:~$ unzip  foo.zip

ANOTHER USE

Along with compression zip can be used to password protected archive.

aon@ox-Vostro-1550:~$ zip -e -r foo.zip foo

It will ask password for encryption.