A "Basic Raver" is a raver who is basic. It is a derogatory term for someone who listens to extremely mainstream electronic music and/or goes to shows/festivals/raves of the same genre for the main purpose of being part of the scene.
Non-basic ravers are generally nice, considerate, friendly and don't care who is watching, they're usually just getting down to the music.
Basic ravers are usually at shows to be seen, start fights, get fucked up and try to get with scantily-clad, sometimes underage, basic raver chicks. Basic ravers will usually take at least 15 shitty photos and multiple videos of the DJ booth from way too far back to even tell what is going on while obscuring your view and simultaneously not realizing or caring that they're elbowing you in the face.
Basic raver chicks especially love taking selfies and 80% of the time, they have duck face everytime. These photos are immediately uploaded to every social media outlet possible and often tweeted at Tiesto ("I'm pretty for Tiesto!"). The guy loves his fans, but these days he's totally catering to basic ravers.
Example 1
A: Daaaaammmnnnn, did you see that chick with the pasties????
Y: Ya bro, she was smokin' hot! I talked to her earlier and she told me she is a senior in high school and then asked me what a "drop" is!!
A: Haha, I love basic raver chicks!!!
Example 2
Tiesto: I am raking in an insane amount of cash and it is all thanks to basic ravers!
Avicii: Bro, you put in your time being about the music... now it's time to make that $$$$$$$$!! LEVELS BRO!
Example 3
Basic 1: Dude, I am so psyched, my dad just bought me a ticket to Ultra! I can't wait to get wasted and see Avicii!!
Basic 2: Me too! Now let's listen to this sick Deadmow 5 track!