Ordinary Time is the name given to the 33 or 34 weeks (depending upon Easter) in the course of the year apart from Advent/Christmas and Lent/Triduum/Easter. Ordinary Time is that part of the liturgical year when no particular moment or aspect of the Christian mystery is celebrated.
Ordinary Time has two phases, a shorter one in winter between the Season of Christmas and the Season of Lent and a longer one through the summer and fall between the Season of Easter and the Season of Advent. The pre-Lenten phase begins the Monday after the Baptism of our Lord. Ordinary Time is then interrupted on the Tuesday before Ash Wednesday for the Seasons of Lent, Triduum, and Easter. It resumes the Monday after Pentecost and continues until the end of the Church year. This second phase includes Trinity Sunday (the Sunday after Pentecost), the Body and Blood of Christ (the Sunday after Trinity Sunday), and Christ the King (the last Sunday of the Church year).