In a fugue stretto is the device by which a second voice enters with the subject overlapping a first voice, rather than starting after the completion of the subject by the first voice. The word is sometimes used to indicate a faster speed, particularly at the climax of a movement.

Pertaining to the fugue, the overlapping of the same theme or motif by two or more voices a few beats apart.

  quickening the speed Also means overlapping entries of a fugue subject.

1) Piling up of fugal entries so that voices enter before the previous voice has completed its statement. 2) Fast concluding section.

[2] imitative counterpoint

 – tight, narrow; i.e., faster or hastening ahead; also, a passage in a fugue in which the contrapuntal texture is denser, with close overlapping entries of the subject in different voices; by extensi [..]

In a fugue, beginning an entry of a subject before a previous entry has finished.

[It] quickening.

Quickening the speed

(music) The presence of two close or overlapping statements of the subject of a fugue, especially towards the end. (music) An acceleration in the tempo of an opera that produces an ending climax. [..]