Which term refers to a tempo that is not as fast as allegro?

The term that refers to a tempo that is not as fast as allegro is allegretto. Allegretto is typically understood to denote a moderately fast tempo, slightly slower than allegro but faster than andante. This makes it a suitable and commonly used tempo marking in various musical compositions, allowing for a lively yet controlled pace.

In contrast, the other options represent different musical terms or qualities: lamentoso conveys a sense of lamentation or sorrow in the music, vivace indicates a lively and brisk tempo that is actually faster than allegro, and largo suggests a very slow tempo. Understanding these distinctions in tempo markings aids musicians in interpreting the intended character and style of a piece effectively.