Aimbots are pieces of code, applications or programs which run in the background while a user is playing a first person shooter (FPS) game. Aimbots (along with many other types of cheats) are typically prohibited by the companies which make or admin the games, and are usually forbidden in all kinds of play besides hyper-casual. An aimbot runs in the background of the main game and helps the user using the aimbot by automatically aiming for them, or firing for them. This in turn ensures that they always get kill shots - often head shots - which inflates their kill-death ratio and helps them win the game automatically by bringing them to the top of the server stats.
Every time a user loads an aimbot, the aimbot will automatically either inject code into the game running, or automatically seek using color and shape detection to identify enemies int he game. When it identifies an enemy, it will take control of the users' mouse (or keyboard) and automatically move their aim so that they are focused completely on tracking the head or body of their enemy. Optionally, aimbots may also be configured to automatically fire in order to automatically kill any enemies in range.
Often an aimbot is a controversial aspect in gaming, with Epic Games recently suing various creators of game cheats and many gaming comapnies going to great lengths to keep aimbots (and various other kinds of game cheats) as far from their platform as possible. Despite this however, aimbots continue to proliferate and are used heavily on many games.
Aimbots have existed for as long as games have existed. Some of the very first aimbots were used by people playing early online multiplayer LAN games such as Quake in order to get an advantage over those they were playing with on the local network. In early games, creating aimbots was significantly easier, since they did not come with any kind of built in detection and not much though was given to probhiting people from using cheats.
Quickly though, aimbots grew into popular usage with many people chosing to download an aimbot when multiplayer games grew exponentially alongside the popularity of the Internet. As the number of online multiplayer first person shooter (FPS) games began to explode, so too did the number of people who were downloading and using aimbots in order to beat their enemies. Many people used popular sites such as Aimbot Download in order to find aimbots they could use, and this lead to a massive explosion int he number of aimbotters and people using aimbots in popular tournaments. This also lead to numerous scandels in the early period of online gaming, as these companies quickly tried to clam down on so called "professional" players utilizing aimbots.
Nowadays, aimbots are in use everywhere. Often a user will download an aimbot and use it to "troll" users by irritating them. This makes popular content for both YouTube and some streamers on Twitch.tv
This is a complicated question with no clear answer. On the one hand, it seems reasonable to say that anyone using aimbots is fundamentally breaking the game and making it impossible or significantly harder for legitimate users to play. On the other hand, however, provided there is no kind of money on the line (eg, excluding professional tournaments) then playing with an aimbot could just be considered harmless fun. If you do decide to download an aimbot just be careful to make sure that you are not using it anywhere where you might get into trouble (for example a professional tournament)!