From LQWiki

The owner of a file or folder is usually the one that created the file, or was specified whilst changing permissions using the chown command. The owner can perform any operations on a file they wish such as read, write, modify, delete. You can determine the owner of a file using the "ls -l" command.

Example:

%ls -l
total 12345
-rwx-r--r--   1 tom users   1028 2006-12-01 00:00 Bobs file

In this example "tom" is the owner, he belongs to the group "users". "-rwx-r--r--" describes the permissions for the file "Bobs file".

You can change the owner of a file using chown.