Chromatic Homotopy Theory
《Chromatic Homotopy Theory》 · 第 287 页 · Section 9.2.11，Essential discs 开头
Let \(M\) be a compact 3-manifold with (possibly empty) boundary. A properly embedded surface \(S\subset M\) is \(\partial\)-parallel if it is obtained by slightly pushing inside \(M\) the interior of a compact surface \(S^\prime\subset\partial M\), possibly with boundary.