The level of demagnetizing force that would need to be applied to a tape or magnetic particles to reduce the remanent magnetization to zero. Measured in Oersteds.

A demagnetizing field of a level in excess of the coercivity must be applied to a magnetic particle in order to coerce it to change the direction of its magnetization. Coercivity is the property of a tape that indicates its resistance to demagnetization and determines the maximum signal frequency that can be recorded by a tape.

Hc is the common abbreviation for coercivity.