Actually, the "sus" is short for "suspended" and causes the 3 note of the
1-3-5 notes in the major chord to be displaced downward (sus2) or
upward (sus4).

Thus, for example, a Cmaj chord (C-E-G) would become Csus2 (C-D-G) or
Csus4 (C-F-G).

Hope this is of use.

Dave