半圆形后殿（法语：Abside,英语：Apse）在建筑学上是指一个覆盖着半球形拱顶或半圆顶的建筑体。对于罗马，拜占庭和哥特式的基督教修道院、主教座堂和教堂建筑，该术语适用于东端主楼的所有半圆形或多角形后殿，不论其屋顶形状是平的，倾斜，圆顶，或半球形。比如在天主教的西欧主教座堂建筑中，该部分是整个主教座堂建筑中不可或缺的。

后殿为半圆形隆起，可以加上半圆顶（也称为半圆顶）或辐射状拱顶。一个简单的后殿很可能只是嵌入到墙的东端。东正教教堂可能有三重后殿，通常标志着拜占庭的影响。

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.