SymmetricMatrixQ[m] tests whether m is a symmetric matrix.

SymmetricPolynomial[k, {x_1, ..., x_n}] gives the k\[Null]^th elementary symmetric polynomial in the variables x_1, ..., x_n.

SymmetricReduction[f, {x_1, ..., x_n}] gives a pair of polynomials {p, q} in x_1, ..., x_n such that f == p + q, where p is the symmetric part and q is the ...

SynchronousInitialization is an option for Manipulate, DynamicModule, and related functions that specifies whether or not to evaluate the expression given as the setting for ...

SynchronousUpdating is an option for Manipulate, Dynamic, and related functions that specifies whether or not to evaluate their contents synchronously.

SyntaxForm is an option for InterpretationBox and TagBox objects that specifies the precedence level to use when the InterpretationBox or TagBox is considered as an operator.

SyntaxInformation[f] gives information used to generate syntax coloring and other advisories when f[...] is entered as input.

SyntaxLength["string"] finds the number of characters starting at the beginning of a string that correspond to syntactically correct input for a single Mathematica expression.

SyntaxPacket[integer] is a MathLink packet where integer indicates the position at which a syntax error was detected in the input line.

SyntaxQ["string"] returns True if the string corresponds to syntactically correct input for a single Mathematica expression, and returns False otherwise.