Its basically people wearing things everyone swore off in the late 90's early 2000's and are now ironically making them cool.
Urban Dictionary: A subculture based on conscious, artificial adoption of things that are in widespread use, proven to be acceptable, or otherwise inoffensive.
Vogue: the notion of dressing in an utterly conventional, nondescript way. Bland anti-style.
K-Hole (Trend Forecasters):
Normcore moves away from a coolness that relies on difference to a post-authenticity that opt into sameness.
Founder of K-Hole, Emily Segal said, "There's an exhaustion with trying to seem different. People are genuinely tired by the fact that to achieve status you need to be different from everyone else around you.
My take: stop stressing out about what you look like and trying to come up with the most interesting outfit. Throw on jeans and a t-shirt. I'm not saying you have to take it to the extreme and walk around looking like Jerry Seinfeld, but relax.
So dig out your old Fruit of the Loom undies, velcro strapped Adidas sandals, and even those Birkenstocks.
flannel, light denim, pullovers and sneaks.