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n. arched recess (particularly one located at the eastern end of a church)

APSE standing for Ada Programming Support Environment is a program or set of programs 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.
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This article is about an architectural feature; for the astronomical term see apsis. For the rock band, see Apse (band). Or you may mean the acronym APS. In architecture, the apse (Latin absis "arch, vault"; sometimes written apsis; plural apses) is a semicircular recess covered with a hemispherical vault. In Romanesque, Byzantine and Gothic Christian abbey, cathedral and church architecture, the term is applied to the semi-circular or polygonal section of the sanctuary at the liturgical east end beyond the altar. Geometrically speaking, an apse is either a half-cone or half-dome.
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Noun
1. a domed or vaulted recess or projection on a building especially the east end of a church; usually contains the altar
(synonym) apsis
(hypernym) recess, niche
(hyponym) tribune
(part-holonym) church, church building

n. abscess, localized collection of pus accompanied by inflammation, gathering, pustule

(n.)
The bishop's seat or throne, in ancient churches.
  

(n.)
A reliquary, or case in which the relics of saints were kept.
  

(n.)
A projecting part of a building, esp. of a church, having in the plan a polygonal or semicircular termination, and, most often, projecting from the east end. In early churches the Eastern apse was occupied by seats for the bishop and clergy.