piano chord
Csus4
C1F4G5
The third replaced by the fourth, which leans on the third it is standing in for.
What is true of it
Csus4 is C, F and G — 1, 4 and 5 counted from C.
These are also the notes of Fsus2/C. Which name is right depends on what is underneath and what came before — the notes alone do not decide.