What is "tight junction"

n. (context biology English) An intercellular junction between epithelial cells whose membranes join together forming a virtual impermeable barrier to fluid

Tight junctions, also known as occluding junctions or zonulae occludentes (singular, zonula occludens), are the closely associated areas of two cells whose membranes join together forming a virtually impermeable barrier to fluid. It is a type of junctional complex present only in vertebrates. The corresponding junctions that occur in invertebrates are septate junctions.