Suspended chords: sus2 and sus4
A suspended chord removes the third — the note that decides major or minor — and replaces it with a second (sus2) or a fourth (sus4). Csus4 is C–F–G; Csus2 is C–D–G. Without a third, the chord hangs in the air, neither happy nor sad.
The classic move is suspension and release: play Csus4, then let the F fall to E. That 4→3 resolution has powered everything from hymn cadences to the opening of "Pinball Wizard". The 7sus4 chord (C–F–G–B♭) does the same trick over a dominant, and is a staple of funk and gospel keyboard playing.
Sus chords also work as destinations, not just tension: much of modern pop and worship music sits on sus2 voicings precisely because they are stable but not sweet. Try replacing a plain major chord with its sus2 in a progression and listen to how much more open it feels.
