Hair Glossary

Anagen effluvium refers to hair shedding that arises during the anagen or growth stage of the hair cycle.

This is in contrast to telogen effluvium or hair shedding that arises during the telogen or resting stage of the hair cycle. 
Anagen Effluvium Is Tied To Chemotherapy Treatments
Anagen effluvium hair shedding is tied to chemotherpay or radiation treatments for various forms of cancer. 

Most chemothrapy drugs work by attacking rapidly dividing cells. Rapid cell replication is one of the hallmarks of cancer; however, hair follicle cells also grow and divide quickly. Consequently, the chemotherapy drugs usually inhibit hair growth.
The dose and type of medicine will determine the severity of hair loss. Once the course of chemotherapy has ended, new hair growth may begin after three to 10 weeks

There are four known cycles or phases for human hair. 
These include:
Anagen -  Growth Phase
Catagen - Transisition Phase
Telogen  - Shedding Phase
Exogen -  The hair exits the follicle