The Gith is a 5e dungeons and dragons monster type that originated in the first edition dungeons and dragons Fiend Folio monster book which was produced by the UK arm of TSR.
The Githyanki (one of two fractured sides of the same race) adorned the Fiend Folio cover and has been a classic monster since – and since the publishing of the 5th Edition’s Mordenkainen’s Tome of Foes both the Githyanki and Githzerai became available character races. The Gith also appear to be an available player option in Baldur’s Gate 3 computer game.
The term Githyanki first appears outside Dungeons and Dragons in George R.R. Martin (yes the Game of Thrones author) in his 1977 novel called Dying of the Light. Reputably the name was later submitted to White Dwarf by a reader of the book who used the same for a fictional race in his homebrew game.
Gith Lore Video Resources
Gith Adventures / Supplements
Harvesters of Worlds: A 1st to 20th Level Githyanki and Mind Flayer Campaign Outline by Sly Flourish (Mike Shea)