The infinity symbol in math represents the concept of infinity. Typically, the symbol is used in an expression like this:
In plain language, this expression represents the limit of the expression as the variable approaches infinity.
The limit operator describes the result of an expression as a variable approaches a value. The operator is used in calculus to formalize what mathematicians mean by approach.
A series is the operation of adding an infinite number expressions together. A series is denoted using the summation operator and the index variable k.