Somebody tell this non practicing Catholic, but not a non thinking person, what Advent is
A calender?
A religion?
Advent is the Season in the (Christian) Church year that precedes Christmas.
The church (liturgical) year is divided up into seasons: Advent, Christmas, Epiphany, Lent, Easter, Pentecost, Ordinary time, Advent. So, first, the Christian Year begins today, the first Sunday of Advent. Advent itself is the four Sundays before Christ's birth (25th) so, it can start as early as November 27 and as late as December 3. On each of the four Sundays of Advent a candle is lit for each of the four Sundays which are (in the Presbyterian Tradition at least) called, respectively, the Sundays of hope, peace, love and joy. They are part of an Advent wreath. Three of the candles are purple (or blue) and the candle of love (third week) is typically pink. (In the Catholic tradition the Third Sunday would be "relaxed" in terms of strictness. There is a liturgy accompanying the lighting of the candles. In the centre of the wreath is a white candle - the Christ Candle - lit on Christmas day.
The liturgical colour of Advent is Purple (or blue) signifying Royalty. It is the same colour as Lent. (BTW the other three colours are white (Christmas/Easter) Red (Pentecost (coming of the Holy Spirit as tongues of fire)) and Green (ordinary time - the rest of the year)
Some countries (particularly European) also have a tradition of Advent Calenders. This are the 25 days before Christmas - counting down. They typically have bags or compartments with little gifts or chocolates behind. So, for instance, I grew up with an Advent Calender as well as Advent in my church.
Hope this makes a bit of sense. Feel free to ask other/ more questions - knowing among other things that terms like Epiphany are not in typical usage much any longer.
