I was taught that in a sus chord the sus replaces a note, usually the third, i.e. C-D-G or C-F-G.

An add chord a note is added to the chord, i.e. C-D-E-G or C-E-G-D, C-E-F-G or C-E-G-F. Note that the first chord in each example can be called a cluster chord.

Whenever I get something stuck in the back of my throat, I dislodge it by drinking a beer.
It's called the Heineken Maneuver.

64 bit Win 10 Pro, the latest BiaB/RB, Roland Octa-Capture audio interface, a ton of software/hardware