Dsus4
Notes: D – G – A — 1 – 4 – 5 (suspended chord: the third is replaced by the fourth)
The "sus4" replaces the third with the fourth (here G instead of F#/F): the chord says neither major nor minor, it stays suspended, with a tension that naturally pulls toward a resolution to D. You'll hear it mostly in pop/folk intros and phrase endings, played right before the D chord itself.
Every sheet in the catalog that uses the Dsus4 chord, across all styles and levels. The same chord comes back in very different contexts — a blues grid, a pop turnaround, an arpeggio sequence: a good way to review it without always playing the same thing.