A Brief History
Dungeons and Dragons is viewed as the first role-playing game of all time, created in 1974 by Gary Gygax and Dave Arneson and published by a company called Tactical Studies Rules, formed by Gary Gygax and Don Kaye. By 1981, the game had attracted over 3 million fans, and by 1989, the second edition of D&D game out, abbrevieted as D&D 2e. In 2000, their company made D&D 3e, published this time by Wizards of the Coast. They released a revised version, 3.5e, in 2003. In 2008, 4e came out, designed by Mike Mearls. And in 2014, the most recent version of D&D, fifth edition, was released.
An Overview
Dungeons and Dragons is a role-playing game, where the players design a character and play them, like a role. There are many different customization options to make each character unique. Characters have races, classes, subclasses, background, and personalities. More detail on those later. Characters start at level 1 and can get all the way up to 20. Games of D&D are not short and can last many, many sessions. Games have some players, and one person who is called the Dungeon Master, or DM, who functions as the narrator. D&D is a group game, and at least 4 people are usually needed. So, grab some friends and start playing!
Diverse and Plentiful
While usually played in a medieval setting, Dungeons and Dragons has rules for other themes. Rules for guns, futuristic weapons, and more is readily available. Not only that, but many official extensions to the core game rules have been added. Some examples are the books Volo's Guide to Monsters and Xanathar's Guide to Everything, but there are many more! On top of that, the community has made countless custom monsters, races, classes, weapons, and more! These custom-made implements are called "homebrew."