Did You Know: Pandemic Phases of Influenza

This is taken off of the WHO site, there's a link at the end of the post for a full detail.
This blog post has only the meaning of each phase.

Phase 1: No animal virus that could cause influenza among humans

Phase 2: Virus circulating among wild and domesticated animals. Known to infect humans and possible pandemic threat.

Phase 3: An animal or human-animal influenza that has caused sporadic cases. No human to human transmission.

Phase 4: Human to human transmission of the virus that can cause a community level outbreak

Phase 5: Community level outbreaks in two countries and one WHO region.

Phase 6: Phase 5 + community level outbreak in one other country of another WHO region

Post Peak Period: Level of pandemic influenza has dropped below peak levels, when under surveillance

Post Pandemic Period: Level of influenza has returned to that of the peak of seasonal influenza in most countries when under surveillance

H1N1 influenza has reached phase 6 pandemic.

Link: http://www.who.int/csr/disease/influenza/GIPA3AideMemoire.pdf