A modem game requires a PC with either an internal modem or external modem connected to it. Back in the 1990s before DSL, Cable, FibreOp was everywhere, this was how you played PC games via multiplayer.

You'd host a connection on your phone line (using the PCs modem) and another friend a few streets away from you would dial your number within the options of whatever game you were playing (such as Warcraft 2, Heretic, Duke Nukem 3d, Doom, Hexen... etc) and connect to you. Of course, they'd also need a modem to do this.

It was extremely popular for its time, though often times with games such as "Duke Nukem 3D" the dreaded, "out of sync" would cause massive frustration.
"Dude, me and Garrett were just playing a modem game of Duke 3d and i kicked his ass!"
by Steve (S.G.B.) December 21, 2016
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