A smurf account is a highly skilled player using a fresh new account in order to prey on newbies (since it's going to be matched with other relatively new and/or low skill accounts) so it can reach high ELO levels super fast, then usually sold online. They're also used in some other games to carry low-level players (either friends or somebody paying) through ranked.
Smurfing is when an expert player creates a new account (the game is F2P) to play with noobs and get easy wins. Boosting means increasing the rank of your account way over your skill level with various exploits (playing with people that throw on purpose to let you win, let someone else use your account, etc.).
Thanks a lot, guys. I can see why that's considered poor sportsmanship and kinda shitty for highly experienced players to deliberately match against newbies and ruin their day.
Kinda like matching me against an EVO class player in Street-fighter