Action painting, drip painting, luminous fields of color so large that they envelop the viewer while exposing the process of their creation. Abstract Expressionism is not a single style and isn't even consistently abstract. Rather, it is intensely personal painting often on a very large scale that is more concerned with exposing the act of creative invention than in traditions of representation.
The term New York School usually refers to both the younger Abstract Expressionists, sometimes also known as 2nd generation Abstract Expressionists, and artists directly influenced by this movement. This includes both the color field paintings championed by the critic Clement Greenberg, who sought to advance formal aspects of AbEx, and artists like Jasper Johns and Robert Rauschenberg who looked at the heroic nature of Abstract Expressionism with both irony and respect.