数学上，若G为群，H为其子群，而g为G中元素，则

仅当H为正规子群时，左右陪集相同，这也是子群正规性的一个定义。

陪集指某个G中子群的左或右陪集。因为Hg = g ( gHg )，（H的）右陪集Hg和（共轭子群 gHg 的）左陪集g ( gHg )是相等的。因此不规定所使用的子群而讨论一个陪集是左陪集或右陪集是没有意义的。

对于交换群或者记为加法形式的群，陪集可以分别用g+H和H+g表示。

In mathematics, if G is a group, and H is a subgroup of G, and g is an element of G, then

Only when H is normal will the set of right cosets and the set of left cosets of H coincide, which is one definition of normality of a subgroup. Although derived from a subgroup, cosets are not usually themselves subgroups of G, only subsets.