Coercivity is defined as the value of the magnetising field at which the intensity of magnetisation becomes zero. It is also known as coercive field.
Hence, the coercivity of a material is a measure of the strength of the reverse magnetising field required to finish out the residual magnetism of the magnetic material.
Reference: This article is referred from my authored book “electrical engineering materials” having ISBN 978-81-272-5491-9. In case of any doubt, then comment it.