There are a lot of things that make a band psychedelic. GENERALLY it's any lesser-known bands from the sixties and music that stems from that. While not all lesser-known bands from the sixties were psychedelic, most of them were because everyone was on acid all the time and it reflected in the music. It's difficult to define psychedelic in a general sense, since the genre is largely based on experimentation; there are patterns, however: intense organs, phasing, surreal lyrics, wailing guitar solos, drum rolls, a shit ton of delay, going flat on purpose... that kind of thing.
Check out some bands, you'll catch on eventually ;-)
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