The Monday after the first Sunday after January 6 (the Feast of the Epiphany) marks the first day of "Ordinary Time" in the Catholic liturgical calendar (unless the Baptism of the Lord is celebrated on that day, in which case the first day of Ordinary Time is Tuesday). Ordinary Time is a feature of the liturgical calendar for the Novus Ordo Mass; before the start of the 1970 liturgical year, what is now known as Ordinary Time was referred to as the Sundays after Epiphany and the Sundays after Pentecost.
Ordinary Time encompasses all of those parts of the Church year that aren't included in the major seasons (Advent, Christmas, Lent, and Easter). Because of this, and because of the connotations of the term ordinary in English, many people have the impression that the Church finds these weeks unimportant. Nothing could be further from the truth.
Ordinary Time is called "ordinary" because the weeks are numbered. The Latin word ordinalis, which refers to numbers in a series, stems from the Latin word ordo, from which we get the English word order. Thus, Ordinary Time is in fact the ordered life of the Church. It's appropriate, therefore, that the Gospel for the Second Sunday of Ordinary Time (which is actually the first Sunday celebrated in Ordinary Time) always features either John the Baptist's acknowledgment of Christ as the Lamb of God or Christ's first miracle--the transformation of water into wine at the wedding at Cana.
This is the new order of the Christian year, one in which Christ, the Lamb of God, walks among us and transforms our lives. In the end, there's nothing "ordinary" about that.