Under no circumstances should you ever give access to your account to another person. No systems staff member will ever ask you for your password, and no faculty member will ever need it.
If you need to share files with another individual, there are a variety of ways to do it without sharing accounts. The simplest way is to understand and use the chmod command. If you don't know how this command works, read the man page and/or pick up an introductory UNIX book.
If chmod doesn't quite fit your requirements, the systems staff can set up a system group for you and the people you wish to share files with. It's very simple to do, and affords great flexibility in file sharing, but also requires an understanding of the chmod command. See also the man pages for group, groups, chgrp.
In some extreme cases, we may determine that it's simplest to allow use of a new, group account.
If the individual you wish to share files with does not have an account in the department, try using the FTP server. See the chapter on Network Services for more details.
If you feel that you can't find an acceptable way to share data with an associate and are tempted to share passwords or otherwise give them access to your account ask the systems staff for help. I have never seen a situation that could not be acceptably resolved without sharing access to an account.
Repeat offenses or cases of users deliberately granting long-term access to their accounts to others (i.e., giving someone your password) may result in account termination. You are not entitled to an account if you abuse it and compromise the security of the system.
If a friend from out of town wants to check his/her email, you can offer them one of your xterms, but do not leave them unattended.