Original: The brown rat, common rat, sewer rat, Hanover rat, Norway rat, Norwegian rat, or wharf rat (Rattus norvegicus) is one of the best known and most common rats.
Simplified: The brown rat, common rat, Hanover rat, Norway rat, Norwegian rat, or wharf rat (Rattus norvegicus) is one of the best known and most common rats, and also one of the largest.