Alt
Alt has 2 meanings
Alternate character
Example
I spent a lot of time leveling an alt yesterday
Related Slang
Categories
A lot
Alt is short for "a lot," and is typically used online and in text messages to save space and time when typing.
The abbreviation is rather obscure because "a lot" is already pretty short and it can be confused as "alternative," "alternate," or "altitude." You will most likely only see it used by people who love to abbreviate everything, which is usually tweens and middle-aged adults who want to be cool.
An example of when you would use it is when gushing about how much you love an actor on Twitter. Another example is when lamenting how much you despise Calculus.
Example
I like their new album alt
How well do you know your texting slang?
When a MOBA or MMORPG player says they're going to use their alt, it means they are going to play as a character other than the one they typically use. For example, in League of Legends (LoL), players usually specialize in playing one champion but play others as alts.
Players may switch from their main to an alt for a variety of reasons. For example, in an MMORPG, if a player's main is a higher level than yours, they may switch to their alt when joining you on a low-level quest, so the quest remains challenging. Players also use alts to experiment with new playstyles and access additional in-game content (e.g. class-specific quests).