An adagio is an indication of movement between the lento (slow) and the andante (when walking).
This Italian term, coming from the expression ad agio meaning at ease, specifies a relatively slow tempo. It corresponds approximately to a range of 56 to 76 beats per minute on the metronome ticks.
As a sonata, concerto or symphony movement, the adagio is most often in the second movement, but some composers have placed it in third. If it can take the form of a simple cadenza as in Bach's third Brandenburg Concerto, its structure is more generally that of the Lied (A - B - A), but it can take important dimensions like the double adagio. theme and variations of the ninth symphony of Beethoven.