Swarming is the process of rapidly Summoning monsters to your side of the field in an attempt to overwhelm your opponent. "Double Summon", "Ultimate Offering", "Cyber Dragon", "The Tricky", and "Gilasaurus" are examples of cards with swarm capabilities. The Six Samurai Archetype is designed to swarm the field to gain power and effects. "Frogs", "Infernity", "Blackwing", "Zombies", "X-Saber", "Dark World" and "Fabled" are also swarm Archetypes.
Anti-Swarm refers to cards that help to counteract Swarming. "Mirror Force", "Summon Limit", "Lightning Vortex" , "Torrential Tribute", "Summoning Curse", and "Dark Hole" are considered Anti-Swarm cards. "Ultimate Tyranno" can aid in defeating swarm monsters on the field, since it has a "Continuous" ability which allows it to attack all monsters on your opponent's side of the field. "Worm Warlord", while not as powerful, can attack twice if it destroys a monster, and it negates their effects, allowing you to get rid of Swarm monsters with annoying effects. However, provided that the swarm monsters are strong enough, "Covering Fire" can land anti-swarm monsters into a near-disadvantage. Several Equip spells, such as "United We Stand" assist swarm decks, while others, such as "Fighting Spirit", work against swarm decks.
Sometimes swarming can lead to overextending.