They just forward you to a generic page full of ads now. This should have 100+ ups, but millineals don't get it because you don't really see 404 pages anymore.
For the #kidsthesedays:
A 404 was what happened if you visited a dead link or something on the web. The equivalent of a "dead end" sign if they put it after you got to the end of the road, and the road had nothing on it to begin with.
[Insert cheeky meme here]