This tag indicates that several equations (of some type) must all hold. Do not use alone! Use in conjunction with (linear-algebra), (polynomials), (pde), (differential-equations), (inequalities) or another tag that describes the nature of the equations being considered.
Other tags in conjunction with this tag should specify, whether the equations of the system are linear, polynomial, ordinary or partial differential equations (or something else). This tag has not fully matured yet. See this meta thread for more opinions and discussion.