Easy question regarding symbols in discrete mathematics

[shamieh]

is the set of symbols that make up strings denoted by the symbol Σ or Σ* , also what is this difference?

 

[Evgeny.Makarov]

Usually the set of symbols, or the alphabet, is denoted by $\Sigma$. Then $\Sigma^*$ denotes the set of all finite strings in the alphabet $\Sigma$.

 

[I like Serena]

The star (*) is the so called Kleene Star.
It means zero-or-more.

So indeed, Σ is the alphabet, while Σ* is the set of strings consisting of zero or more symbols from the alphabet.