As I understand it, the original martini was 1 part sweet vermouth to three parts gin. That's a lot of vermouth.
A dry martini used dry vermouth instead of sweet, in the same proportions.
So what most people drink today isn't a martini. They're just drinking an ice cold glass of gin with an olive. Same thing, of course, with a vodka martini (which isn't really a martini any more than an "appletini" is, or any of the chocolate martinis or other flavors you find on some martini lists).