Absolute path is the complete path of a file or directory from the root directory. In general root directory is represented by / symbol. If we are in a directory and want to know the absolute path, we can use pwd command.
Relative path is the path relative the current location in directory.
E.g. In a directory structure /var/user/kevin/mail if we are in kevin directory then pwd command will give absolute path as /var/user/kevin.
Absolute path of mail folder is /var/user/kevin/mail. For mail folder ./mail is the relative path of mail directory from kevin folder.