Definition:String

Let $$\mathcal{A}$$ be an alphabet of symbols.

A string (in $$\mathcal{A}$$) is a series of symbols from $$\mathcal{A}$$ placed one after the other.

There is no limit to the number of times a particular symbol may appear in a given string.

Finite String
A finite string is a string with a finite number of symbols in it.