Seised or seized comes from the French verb saisir and means to grasp, seize or grip. In the legal context it means that an entity, usually a court, has decided that it will consider a legal matter or issue falling within its jurisdiction. The spelling is variable, with English usage tending towards seised, North American towards seized, seized being the predominant spelling today.
The expression is formally used in Articles 27-30 the Brussels Convention with respect to the Lis Pendens rule.