Six figures simply refers to a salary with six digits (i.e. in excess of $100,000). This is nearly double the median income so "six figures" is often just used to mean "a lot of money."
"Six figures" appears to be an idiom in American English that should be abandoned.
Six figures simply refers to a salary with six digits (i.e. in excess of $100,000). This is nearly double the median income so "six figures" is often just used to mean "a lot of money."