Q: what's sus?
A: for example, if you have a C major chord (with notes C, E, and G) and you swap out the E note for F instead (C, F, G), this new chord would often be considered Csus4. If you swap the note for D instead (C, D, G), it might be considered Csus2. If there is no number in the chord symbol and it just says Csus, it would almost definitely be assumed to be Csus4. but if you're a person who uses both sus2 and sus4 frequently, it's probably good to specify the number