The gt number is one of the two most important unique numerical identifiers associated with a Georgia Tech student. The student number is the other and is treated elsewhere. The gt number is, in fact, not a number: the gt number of a student is an alphanumeric string of the form:
where ? represents a letter and # represents a digit from 0-9.
The gt number is most notably the name of a student's account in all OIT computer labs (Georgia Tech public computer labs). This means that the student's email address is of the form email@example.com, and their home page is http://prism.gatech.edu/~gt?###?/ . The student also uses their gt number to log into acme (acme.gatech.edu), which is a Solaris server (technical note: actually three loadbalanced servers) used mainly for remote access and to change the password for your gt account (the account associated with a gt number).
The gt number is extremely useful because it makes collection of email addresses easy for student organizations. However, most students choose to use an email alias for exchange with those who are off-campus. Most of them are provided by ResNet (resulting in a firstname.lastname@example.org address), but some other orgainizations (such as SGA) provide their own.
Faculty also have gt numbers, but they are slightly different:
Where f is the first initial and l is the last initial of the faculty member, and # represents a digit from 0-9. These are almost never given to students; instead, most faculty provide a email@example.com address.
There are some instances of other, unexplained gt numbers that do not fit the above patterns, such as gt####, which is of unknown use but does exist. Rumor has it that people with these gt numbers have simply been at Tech for too long.