Occlude means to obstruct, as with an opening. You hear this a lot in a medical context. Heart surgeons are looking for occlusions in blood vessels — things that occlude the flow of blood.
Occlude does not exist only in a medical context. If you close the bathroom door so your little brother won't come in while you're trying out makeup with your friends, you're occluding the bathroom. Meanwhile, your makeup occludes your pores.