A "serious game" is one that intends
more than entertainment for its players

Serious games generally aim to teach or train, often by realistically simulating some aspect of a world system. Examples include: business training games, disaster preparedness games, flight or driving simulators, games that help patients understand how their bodies are fighting an infection or cancer, and so on. Serious games can be very effective at education, because they allow players to test and experiment with systems, which leads to better understanding of the relationships that comprise the system.

An "alternate reality game" is an interactive, transmedia narrative that evolves in response to what its players do

An alternate reality game (ARG) "is an interactive narrative that uses the real world as a platform, often involving multiple media and game elements, to tell a story that may be affected by participants' ideas or actions. ARGs are typified by intense player involvement with a story that takes place in real time and evolves according to participants' responses, and with characters that are actively controlled by the game's designers. ARGs generally rely on the Internet as the central binding medium" (Wikipedia). ARGs are attracting attention because they have been able to engage large numbers of players in collaborative efforts to solve very difficult puzzles and challenges.