There are actually three types of sweepers: Mixed, Physical, and Special Sweepers.
Sweepers in general are fast and have high offensive stats in at least one of the attacking stats. Physical and Special Sweepers also have access to a stat boosting move in theirfield of offense, such as Swords Dance for Physical and Nasty Plot or Calm Mind for Special. Mixed Sweepers however have large Attack and Special Attack and a number of options for both. They are able to take down most types of walls due to this. Common Sweepers are Porygon-Z, Lucario, and Infernape.