Question

what is mean by Hydra

Answer 1

Hydra are truly fascinating small aquatic animals. Most hydra are tiny, reaching a maximum of only about 30 mm long when fully extended. They are barely visible to the naked eye and a hand lens or microscope are needed to be able to see them properly. When the body is extended with the tentacles waving in the water, they resemble a small piece of string which has become frayed at one end. If disturbed, a hydra will contract its body and tentacles, so that it now resembles a small 'blob'.
They can be found in freshwater ponds and slow-moving rivers, where they usually attach themselves to submerged plants or rocks.

Answer 2

Hydra is type of organism belonging to kingdom animalia