What does Hare come from?

Govinda is the name of Shri Krishna. Literally it means the protector of cows. The name is derived from an incident in the life of teen-Krishna. The people of his clan used to pray Indra, the God of rain. He asked them to stop worshipping Indra and start worshipping the hill, which is the source of grass for their cattle and of water for them and of many medicinal herbs. This irritated Indra who made hell-storm for 7 days. Krishna lifted the hill to shelter the clans men and the cows. Indra accpeted defeat and named Krishna as Govinda.
Hare is a form of the word Hari used in calling somebody. (Its equivalent to "O Hari")
Gopala again is a name of Krishna meaning the inhavitant of the village Gopa.
So Govinda hare gopala hare means calling the lord using these three names.