A Roman divinity presiding over boundaries and frontiers. His worship is said to have been instituted by Numa who ordered that every one should mark the boundaries of his landed property by stones to be consecrated to Jupiter, and at which every year sacrifices were to be offered at the festival of the Terminalia. (Dionys. ii. 9, 74.)
These sacred boundaries existed not only in regard to private property, but also in regard to the state itself, the boundary of which was not to be trangressed by any foreign foe. But in later times the latter must have fallen into oblivion, while the termini of private property retained their sacred character even in the days of Dionysius, who states that sacrifices of cakes, meal, and fruit (for it was unlawful to stain the boundary stones with blood), still continued to be offered. The god Terminus himself appears to have been no other than Jupiter himself, in the capacity of the protector of boundaries. (Fasti By Ovid ii. 639, &c.; Lactant. i. 20, 37.) The Terminus of the Roman state originally stood between the fifth and sixth milestone on the road towards Laurentum, near a place called Festi, and that ancient boundary of the ager Romanus continued to be revered with the same ceremonies as the boundaries of private estates. (Fasti By Ovid)
Another public Terminus stood in the temple of Jupiter in the Capitol, and above it there was an opening in the roof, because no Terminus was allowed to be under cover. (Fest. p. 368, ed. Müller.) This is another proof that Terminus was only an attribute of Jupiter, although tradition gave a different reason for this circumstance; for when that temple was to be founded, and it was necessary to exaugurate other sanctuaries standing on the same site, all the gods readily gave way to Jupiter and Juno, but the auguries would not allow the sanctuaries of Terminus and Juventas to be removed. This was taken as an omen that the Roman state would remain ever undiminished and young, and the chapels of the two divinities were inclosed within the walls of the new temple. (Serv. ad Aen. ii. 575, ix. 448; Ov. Fast. ii. 671.)
Here we may ask, what had a Terminus to do on the Capitol, unless he was connected or identical with Jupiter? (Comp. Liv. i. 55, v. 54, xliii. 13, xlv. 44; Polyb. iii. 25 ; Hartung, Die Relig. der Röm. ii. p. 50, &c.)From Smith's Dictionary of Greek and Roman Biography and Mythology
From Fasti By Ovid
Though January is the first month, and was before,
February that follows was once last in the ancient year.
And your worship, Terminus, closed the sacred rites.
The month of Janus came first, being the entrance (janua):
This month was last, sacred to the last rites of the dead.
Afterwards the Decemvirs are thought to have brought together
These months that had been parted by a wide interval of time.