For everyday purposes seizures are broadly categorized as either generalized or focal in onset, these terms can be used where appropriate, but there are seizures that cannot be categorized in this manner and are classified as having unknown onset. Seizures with unknown onset can be further classified as motor (for example epileptic spasm, tonic-clonic), or non-motor (for example, behavior arrest) in type.
A seizure may be unclassified due to inadequate information to allow it to be placed in the focal, generalized or unknown onset categories. This may occur if it was not witnessed at onset, and if results of investigations (such as EEG and imaging) are not yet available.