ah, I think that's more confusing.

A "sus" chord is just a chord with no third, and a fourth or second in place of the third.

"sus" by itself means the suspension is a fourth. If the suspension is a second, then the chord is labeled "sus2".
here are some examples, and their spellings:

C -- C E G

C sus -- C F G

C sus4 -- C F G (same as C sus)

C sus2 -- C D G

hesperis, the "sus" convention only applies to seconds and fourths, if you want to add a ninth to a chord with no seventh, it's designated as (chord name) add9.

just in case someone else posts while I'm typing this, the "more confusing" bit at the top refers to hesperis' post.