What is the method swarm in Pokemon Platinum?

In battle

Swarm strengthens bug-type moves in a pinch. When a Bug-type move is used, it will do 1.5× its usual damage if the user has less than one third of its HP remaining. It can be considered the Bug-type variation of Blaze, Overgrow, and Torrent.

If the Pokémon leading the party

has Swarm, the chance of encountering wild Pokémon increases.