What does "tonic" mean in relation to epilepsy?

What does "tonic" mean in relation to epilepsy?

Charles Ribak, Ph.D. (Professor of Anatomy and Neurobiology, UC Irvine School of Medicine) gives expert video advice on: What is a "photosensitivity" seizure trigger?; What is an "automatism"? and more...

With epilepsy, ‘tonic' refers to the powerful muscular excitation that occurs throughout the body. So, in our normal movements, we have a flexor and an extensor muscle around every joint, with one of these muscles relaxing while the other is contracting. During a tonic seizure or tonic activity, we have both muscles contracting at the same time, which leads to both arms and both legs being outstretched. This is due to severe muscular contraction of both extensors and the flexors.