Juno Februtis is an aspect of that great Roman Goddess as a purifier and fertility Goddess, who was especially connected with the month of February and the festivities in its latter half. She would seem to be related to Juno Lucina as a childbirth Goddess. February was the month of purification to the Romans because in their early calendar it was the last month of the year, and so considered an appropriate time to get rid of the bad, stale, or unclean in preparation for the new year. The references to Juno Februtis are few, however, and much of the information about Her would seem to be of more recent derivation.
February takes its name from the Latin februa, meaning "religious purification", and so means "the month of purification", or "the cleansing month", referring to the numerous festivals of that theme held then, especially the Lupercalia. In the early days of the lunar calendar, March, as the month when spring takes hold, had been thought of as the first month of the year; and so many holidays in the last half (the waning half) of February centered around the theme of endings, including the Terminalia on the 23rd, honoring Terminus, the God of boundary stones. The 23rd for whatever reason had a ritual significance as the last day of the year, even though the month (mostly) held 28 days; in a lunar calendar the months are aligned with the moon phases, but since the lunar cycle fits real imprecisely into the solar one (it is off by 11 days), every other year or so, depending on the system, an entire extra month is added to keep it more or less in synch, and the Terminalia had been the traditional time for doing so.
The Lupercalia, held on the 15th, was a very ancient and very popular holiday that included rituals to purify the city of Rome and bring fertility to it. The celebrations were centered on the Palatine Hill, where the twins Romulus and Remus, the legendary founders of Rome, were said to have originally settled. On this day a goat (or goats) and a dog were sacrificed. From the skin of the goats were made loincloths, which were the only clothing worn by certain groups of young men who ran the bounds of the city carrying whips, also made from the sacrificed goats' skin; with these they hit the people they came across. This act was thought to not only drive away the bad but also to draw in the good in the form of fertility for the people and the city in general, and it is said that women hoping to get pregnant or looking for an easy time in childbirth would deliberately put themselves in their way so they could be hit. Plutarch, who lived in the 1st and 2nd centuries CE, when the Lupercalia was in full swing, said that because the Lupercalia was so heavily involved with purification the day was called februata or dies februata ("the day of purification"). (Incidentally in the same passage he mentions a Greek ritual of purification called periskylakismos, in which the person to be purified was rubbed all over with puppies, apparently because puppies absorb bad vibes. Though he doesn't say so the unlucky little guys were probably thought of as scapegoats and sacrificed later to Hekate or somesuch, which is no good at all, no sir! But I don't see why periskylakismos couldn't be revived in a more modern form without the sacrifice. Can you imagine a sillier, more giggly squirmy fun time than to be purified by having someone rub puppies all over you?)
The Parentalia, or festival of the ancestors, was held from the 13-21 of February, and during this holiday offerings were given to the dead, especially on the Feralia on the 21st, when the dii manes, the divine and powerful dead, were propitiated. According to Ovid this was part of the purification ceremonies of the month, because once the dead have had their due, the city can then move on to matters of the living and the season is again clean. (I have always thought it rather nice that on the 22nd, after the ancestors and dead family members had been honored, the Romans turned to the living family and celebrated the Caristia, when family reunions were held and it was traditional to settle family arguments or feuds.) Another one of February's cleansing holidays was the Regifugium ("The Flight of the King") on the 24th, which was said to commemorate when the last King of Rome was driven out and the monarchy gave way to the Republic, a cleansing of a different sort.
Ovid in his Fasti, or account of festivals (written in the early 1st century CE), does not mention Juno Februtis in February as one might expect; he does mention Juno Sospita ("Saviouress") as presiding over the Kalends, or first days of the month, but this is hardly unique as Juno was said to preside over all Kalends. In his entry for the Lupercalia, he refers to Lucina as the childbirth Goddess, praising Her for the fertility of the day. He does, however, go on at some length about the februa, the things used in purification rituals that gave their name to the month. The earliest mention for Juno Februtis I could find was by Arnobius, an early Christian writing around 300 CE who felt it necessary (like some other early Christian authors) to write about how silly or obviously wrong the Pagan religion was when compared to Christianity; in the process of attempting to disprove Juno's existence, he lists many of Her known epithets, and includes Februtis among them. It would seem, then, that this aspect of Juno was a late one, perhaps linking the purification and renewal themes of the month with Her well-known aspect as patroness of childbirth, which involves similar anticipation of the new.
A source from the 18th century claims February 14th as the feast day of one Juno Februata, in an attempt to explain why St. Valentine's Day is concerned with lovers; I suspect this is a misunderstanding or misreading of the phrase dies februata, "day of purification", perhaps mistaking februata for Februtis.
There is also a Roman God by the name of Februus, a Deity dedicated to purification Who was considered the patron God of the month of February. He may personify February's cleansing festivals; and because of the association with the Parentalia and Feralia He was considered a God of the Dead, even to being equated with the King of the Underworld Dis or Pluto. Some modern sources refer to a Goddess called Februa; I could find no mention of Her that wasn't modern. While it's possible that Februus was associated with a Goddess as His female equivalent, the only mentions of februa I could find were as the objects used in ritual purification.
All that said, Juno Februtis would seem to be an aspect of Juno connected with the purificatory rites of February, and the fertility and creativity that can be had when the old is cleared out to make way for the new.
Alternate spelling: Februtis, like I said above, was the only early epithet I could attest, but 19th century sources (specifically William Smith, in his Dictionary of Greek and Roman Biography and Mythology) give Februlis, Februata, Februta, or Februalis as alternates.
She is sometimes erroneously linked with the Goddess of Fevers Febris; though both Their names do ultimately derive from the idea of purification, as fevers were believed to purify the body by burning off disease, They are not related.