What is "cleavage furrow"

n. (context biology English) The invagination of the cell membrane, at the equatorial plane of the cell, that characterizes the onset of cytokinesis in animal cells.

In cell biology, the cleavage furrow is the indentation of the cell's surface that begins the progression of cleavage, by which animal and some algal cells undergo cytokinesis, the final splitting of the membrane, in the process of cell division. The same proteins responsible for muscle contraction, actin and myosin, begin the process of forming the cleavage furrow. Other cytoskeletal proteins and actin binding proteins are involved in the procedure.