This tag collects posts about "relativistic membranes", which are time-like submanifolds of Minkowski space with prescribed (usually vanishing) mean curvature. They model extended (in the sense of higher dimensional, compared to point particles which have 0 dimensions) test objects moving under the balance of external pressure and elastic tension. These objects in the study of high-energy physics and cosmology (cosmological strings, domain walls), and also topological defects of classical fields.