A real action to re-cover the possession of land where the ten-ant (or owner) bas been disseised or other-wise wrongfully dispossessed. If the disseisor has aliened the land, or if it has descend-ed to his heir, the writ of entry is said to be in the per, because it alleges that the defend-ant (the alienee or heir) obtained possession through the original disseisor. If two aiien-ations (or descents) have taken place, the writ is in the per and cui, because it alleges that the defendant (the second alienee) ob-tained possession through the first alienee, io whom the original disseisor had aliened it. If more than two alienations (or descents) have taken place, the writ is in the post, be-cause it simply alleges that the defendant acquired possesslon after the origlnal disseisin
Source: Black's Law Dictionary 2nd Ed (1910)