Biased or when someone is an agreeable person but not specifically that you agree with them. Usually used sarcastically. Also can be used as anything.
An adjective used to refer to a person whose beliefs are made "based on themselves" or what they themselves experienced and like, and not to satisfy others needs.
It can be used positively by just being a typical "be who you want to be and not what they expect you to be" word. It's kind of meant to describe the guy who prefers to die standing than live kneeling to something they see incorrect, to a typical authoritarian government or a crowd that isn't aware of their mistakes or things they did wrong. That is, at least, it's popular definition.
Interestingly enough, the word "Based" can be used to a really high extreme by making the "be who you want to be (^・ω・^✿)" saying get inside a blender, go from white to red, and just be used to describe the guy who wants the germans to bring back hitler, or anything that can be associated with very taboo groups like the KKK or the nazis.
It applies to the word "Based" because these people have an ideology that they themselves have without caring of what others think, it's just that it's now proposing mass murder. Same Shit Different Day.
Note: This slang should be kept inside the shithole. Using it outside the internet will either get you to be friends with weird kids or bullied.
Example 1, used by redditors or twittards with the normie personality trait.
User 1: "I hate oranges, I hate orange man!"
User 2: "Omg so based."
Example 2, used majorly by, most people, average internet users, with average mind personality trait.
User 1: "Why do people call black people as black if they're actually brown?"
User 2: "Omg so based."
Example 3, It's assumed to be used by the "evil hacker known as 4chan" users with antisocial personality trait, or people who just want to say controversial shit because it's fun.
User 1: "Vaporeon is the best pokemon"
User 2: "Omg so based."
Based is a word used when something is agreeable, great, cool, or in extreme cases, even misogonistic or homophobic.
Person 1: Episode 21 of (insert show) is the best episode.
Person 2: Based.
When two people have the exact same damage percentage in a conclave PVP match, but vastly disproportionate kills.
-Same dmg, 26 kills, 12 kills. Based.
-Chase me less next time idk lol cya.
when something is sheesh as fuck
Chad; yo bro im based
Sean: sheesh.
bill: hey did you see what hideki posted
joe: yeah he was based as always