It really depends on application type, but the term "hyperlink" is usually related to a Web application. Sometimes not, but then it's even more trivial and can be… nearly anything.
Good idea. Now, what is so difficult? In its simplest form:
<a href="somethingWhichLogsYouOut">Log out</a>
Everything else depends on how you support authentication, membership and related things, what technology do you use on server side and other things.—SA