What is Aliquid Possessionis Et Nihil Juris?

Legal Definition
Somewhat of possession, and nothing of right, (but no right) A phrase used by Bracton to describe that kind of possession which a person might have of a thing as a guardian, creditor or the like; and also that kind of possession which was granted for a term of years, where nothing could be demanded but the usufruct. Bract, fols. 39a, 160a.
-- Black's Law Dictionary
Legal Definition
Somewhat of possession, but nothing of right.
-- Ballentine's Law Dictionary