x*y*z, xyz or x y z represents a product of terms.
The character is entered as * or \[Times]. It is not the same as \[Cross].
Times has attributes Flat, Orderless and OneIdentity.
The default value for arguments of Times, as used in x_. patterns, is 1.
Times[ ] is taken to be 1.
Times[x] is x.
0 x evaluates to 0, but 0.0 x is left unchanged.
Unlike other functions, Times applies built-in rules before user-defined ones. As a result, it is not possible to make definitions such as 2*2=5.
See The Mathematica Book: Section 1.1.1.
See also: Divide, NonCommutativeMultiply, Dot.