Is a convulsion always from a seizure?

Convulsive seizure: A convulsion is a type of seizure where there is uncontrollable shaking with or without loss of consciousness , frothing of the mouth, incontinence and sleepiness after the episode. There are other types of seizures that don't have convulsions. For example the patient may simply stare blankly and be unaware.

Interchangeable: The terms convulsion ; seizure can be used interchangeably. A convulsion that involves the whole body (sometimes called a “generalized tonic-clonic” or “grand mal” seizure) is the most dramatic type of seizure, causing rapid, violent movements and occasionally loss of consciousness. These sometimes can start with focal (1 side of body) and progress to generalized (both sides).