No, Advent is the liturgical season preceding Christmas, beginning the fourth Sunday before Christmas (which is also the Sunday nearest November 30), it is a period of at least three weeks and one day (the shortest period that can start on a Sunday and include four Sundays.)
The 12 days of Christmas start on Christmas and end on January 5, the eve of the Feast of Epiphany.
12-day advent calendars are a fairly recent invention that mirrors the 12-days of Christmas, but has no direct correspondence to anything in any traditional Christian religious calendar (the more common 24-day format is also a modern, but less recent, invention detached from the religious calendar, that simplifies by ignoring the floating start date of advent and always starting on Dec. 1.)
True, I should have specified that the timing I was providing was the Western tradition; the Orthodox (both Eastern and Oriental, I believe) tradition has a 40-day Nativity Fast (in some, the name is different in others) mirroring the 40-day season of Lent, that is similar (in terms of being a preparatory season for the Feast of the Nativity) to the Western Advent.
The 12 days of Christmas start on Christmas and end on January 5, the eve of the Feast of Epiphany.
12-day advent calendars are a fairly recent invention that mirrors the 12-days of Christmas, but has no direct correspondence to anything in any traditional Christian religious calendar (the more common 24-day format is also a modern, but less recent, invention detached from the religious calendar, that simplifies by ignoring the floating start date of advent and always starting on Dec. 1.)