Murasugi sum

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The union of a finite sequence of surfaces taken over a disk common to every adjacent pair of the sequence, such that the boundary of the disk comprises some even number of closed arcs, disjoint except at their endpoints, which are alternatingly subarcs of the two surfaces' boundaries.
• noun The union of links formed by taking such a sum of their Seifert surfaces and taking the boundary of the result.