What exactly is "Ordinary Time" in the Catholic Church's liturgical calendar? In the Catholic Church's liturgical calendar, there is a period known as Ordinary Time. What is it exactly and what differentiates this period from the others in the calendar.

The answer should also include the origin of the name "Ordinary?" My understanding is that the period is not called Ordinary Time just because the period is "ordinary."
The Ordinary time is a period within the Church's liturgical year that does not celebrate like Christmastide (25 of dic.- sunday after epiphany) or Pascha(Easter sunday-pentecost), nor is penitential like advent(4 sundays before Christmas-24 of dic.) or Lent(Ash Wed.-Holy Saturday). It is a period of Hope and growth in Christ. It occurs two times, the first from Christmas to Lent and the second from Pascha to Advent. It liturgical color is green.

Edit: "Ordinary Time" implies just that it is not seasonal, this page might help you look more in depth 

In Wikipedia it gives a small history of the term


  Before the liturgical reforms of 1970, there were two distinct seasons in the Roman Breviary and Roman Missal, known as the season after Epiphany and the season after Pentecost, respectively. Liturgical days in these times were referred to as the -nth Sunday after Epiphany or Pentecost, or Feria II,III,IV,V or VI after the -nth Sunday.


www.cyberfaith.com/calendar/ordinary.html

Also Eastern Orthodox observe Ordinary Time.