Legato

Legato means connecting notes together without repicking them: on guitar, it almost always relies on hammer-ons and pull-offs. The sound never stops between the two notes, unlike two notes picked separately.

The real gain isn't speed, it's phrasing

Many beginners see legato as a shortcut to play faster. That's a real side effect, but the main point is elsewhere: without a pick attack on every note, phrasing becomes smoother and closer to singing — which is why it shows up as much in slow melodic phrases as in fast runs.

The technique sheet one-string legato — hammer-ons and pull-offs isolates the move on a single string before combining it into a full melody.