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 back's other pulling muscles. Key cue: set your shoulder blades down first and lead with your elbows, so the back pulls.
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.