NSolve[lhs==rhs, var] gives a list of numerical approximations to the roots of a polynomial equation.
NSolve[, , ... , , , ... ] solves a system of polynomial equations.
NSolve[eqns, vars, n] gives results to n-digit precision.
NSolve[eqns, vars] gives the same final result as N[Solve[eqns, vars]], apart from issues of numerical precision.
See The Mathematica Book: Section 1.6.3, Section 3.4.2, Section 3.9.1 and Section 3.9.5.
Implementation Notes: see section A.9.4.
See also: Solve, FindRoot, NDSolve.
Related package: NumberTheory`Recognize`.