The magnetism remaining in the magnetic material, even when the magnetising field is reduced to zero is called residual magnetism. The power of retaining this magnetism is called the retentivity or remanence.
Therefore, the retentivity is also defined as the measure of the magnetisation remaining in the material when the field is totally removed.
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.