the short answer
The lat pulldown is a machine-based vertical pulling exercise where you sit, grip a bar overhead, and pull it down to your upper chest before controlling it back to a full stretch. It builds the lats and the rest of the back's pulling muscles. The single most important cue is to set your shoulder blades down first and lead with your elbows, so the pull comes from the back rather than the arms.
This article is general technique education for coaches and clients, not medical or rehab advice - form is individual, and a qualified coach watching the movement and giving a form check is the gold standard. Clients with pain or a relevant history should clear it with a qualified professional first.