APSE standing for Ada Programming Support Environment was a specification for a programming environment to support software development in the Ada programming language. This represented the second stage of the U.S. military Ada project; once the language was implemented, it was felt necessary to specify and implement a standard set of tools, hence the APSE. CAIS-A, Common APSE Interface Set A, was defined in MIL STD-1838A.

In architecture, the apse (from Latin absis: "arch, vault" from Greek ἀψίς apsis "arch"; sometimes written apsis; plural apsides) is a semicircular recess covered with a hemispherical vault or semi-dome, also known as an Exedra. In Romanesque, Byzantine and Gothic Christian abbey, cathedral and church architecture, the term is applied to a semi-circular or polygonal termination of the main building at the liturgical east end (where the altar is), regardless of the shape of the roof, which may be flat, sloping, domed, or hemispherical.