What is the difference between cancun and cancun-riviera maya?

Cancun is mostly thought of as the island shaped like the number seven that is connected to the mainland by two bridges. That's where the the resort hotels and the best beaches are. The top part of the seven connects to "old" Cancun--the part of the town that was there before the resort construction began. The bottom part of the seven connect to the mainland where the Cancun airport is.
Riviera Maya are all the other towns on that side of the Yucatan peninsula, including:
Akumal
Cozumel
Isla Holbox
Mahahual
Playa del Carmen, Playacar
Puerto Aventuras
Puerto Morelos
Soliman Bay & Tankah Bay
Tulum
South Quintana Roo
Xcalak

One is easier to say.

Cancun-Riviera Maya has a lot of excellent history behind it and Cancun is a city in Mexico.

Hello,
The Rivieria Maya is south of cancun about 30 minutes. Most of the hotels are spread apart vs right next door to each other.

Riviera Maya is the whole coastal region around Cancun.

Cancun is the city proper. Riviera Maya encompasses the region, extending primarily down the coast from Cancun.