The asterisk is a small star symbol used in writing and printing as a reference mark or to indicate an omission. Wikipedia explains that, on the Internet, the asterisk is commonly used to correct spelling in which case it appears before or after the correct word.
The asterisk is often used to call out a footnote, especially when there is only one on the page. They are sometimes used as an alternative to typographical bullet points to indicate items of a list. In computer science, the asterisk is used to denote zero or more repetitions of a pattern. Many programming languages and calculators use the asterisk as a symbol for multiplication.