Quoting Scott Alexander:

A “concept handle” is a memorable noun phrase representing a complex, often abstract topic. For example: “prisoner’s dilemma,” “Overton window,” “belief in belief,” etc.

Successful concept handles can really amplify a vague idea which many people sort of understand but can’t point to and talk about. If you give that vague notion a crisp, catchy name, you can unlock a lot of conversation and reflection.