Best definition
When a large sum of people from a group or multiple groups start flooding into a website or online community.

Often normies, but sometimes other groups. This may be good or bad usually bad. May or may not permanently effect the website/community.

Facebook is immune to webvasion, as it’s already full of normies.

4chan is also immune, as the current community is so disgusting most people leave immediately.

Youtube’s already been webvaded.