In this suspension we delay the resolution to the root (“the 1”) of the major triad by playing “the 2” instead…
Here, for example, is a C Major Rootless Add2 (for lack of a better name) with its resolution:
Notice how unstable and antsy the rootless add2 chord sounds and feels, like it needs to go somewhere, and how that instability is relieved upon the arrival of the major triad.
Suspensions can be applied to add harmonic interest in many musical contexts, for example in “Close to You” (The Carpenters)…