piano chord
Gsus4
G1C4D5
The third replaced by the fourth, which leans on the third it is standing in for.
What is true of it
Gsus4 is G, C and D — 1, 4 and 5 counted from G.
These are also the notes of Csus2/G. Which name is right depends on what is underneath and what came before — the notes alone do not decide.