Can someone explain smurfing?

What I know about smurfing is a high skilled player purposely creates a new account to prey on weaker players?

What about someone who genuinely has a new account for any realistic reason (ex. Lost access to old account or whatever). Said player would be starting from zero but still has experienced skill level. Would this be considered smurfing? Personally I encounter good players a lot of the time and occasionally sweaty players. But never did it occur to me that someone playing way better than me is bad thing.

Im curious because it seems like such a big deal and I don’t fully understand the concept.