It means "playing a game." Gaming also refers to the gaming industry as a whole, which was built upon video and computer games. Some games are available on CD-ROM, while others are available directly online and can be played by more than one user, simultaneously. The software is usually based on traditional game categories, such as adventure, role-playing, or strategy.
Historical perspective: In 2013, the NSA spy agency hacked into and infiltrated online games like World of Warcraft and Second Life to hunt for terrorists, according to documents leaked by Edward Snowden. The NSA assumed that game features like fake identities, text chats, and the anonymous movement of money would appeal to militants. Agents began analyzing in-game communications as early as 2007, reportedly using virtual characters to snoop on targets and recruit informers. The agency was also concerned that some games could “offer realistic weapons training” and military skills. “Some of the 9/11 pilots had never flown a real plane,” the leaked NSA document stated. “They had only trained using Microsoft’s Flight Simulator.”