SEASON AFTER PENTECOST
The season after Pentecost, according to the calendar of the church year (BCP, p. 32). It begins on the Monday following Pentecost, and continues through most of the summer and autumn. It may include as many as twenty-eight Sundays, depending on the date of Easter.
This includes Trinity Sunday which is the First Sunday after Pentecost. The BCP provides proper collects and readings for the other Sundays of the season.
These propers are numbered and designated for use on the Sundays which are closest to specific days in the monthly calendar, whether before or after. For example, Proper 3 is designated for use, if needed, on the Sunday closest to May 25. Proper 29 is designated for use on the Sunday closest to Nov. 23.
Prior to the 1979 BCP, Sundays in this long period of the church year were identified and counted in terms of the number of Sundays after Trinity Sunday instead of the number of Sundays after Pentecost.
Source: https://www.episcopalchurch.org/glossary/pentecost-season/
ORDINARY TIME
This term is used to indicate the parts of the liturgical year that are not included in the major seasons of the church calendar. Ordinary time can be understood in terms of the living out of Christian faith and the meaning of Christ’s resurrection in ordinary life. The term “ordinary time” is not used in the Prayer Book, but the season after Pentecost can be considered ordinary time.
It may be referred to as the “green season,” because green is the usual liturgical color for this period of the church year.
Ordinary time includes the Monday after the Feast of the Baptism of our Lord through the Tuesday before Ash Wednesday, and the Monday after Pentecost through the Saturday before the First Sunday of Advent. A vigil or other service anticipating the First Sunday of Advent on the Saturday before that Sunday would also be included in the season of Advent. The BCP provides numbered propers with collects and lectionary readings for the Sundays of the Season after Pentecost. The Epiphany season includes the Epiphany, the First Sunday after the Epiphany: the Baptism of our Lord Jesus Christ, and the Second Sunday through the Last Sunday after the Epiphany (BCP, p. 31).
In view of the Epiphany themes that are presented throughout the Epiphany season, it should not be considered ordinary time. However, many parishes use green as the liturgical color for the Second Sunday through the Sunday prior to the Last Sunday after the Epiphany, and sometimes the Last Sunday after the Epiphany. Epiphany season and the season after Pentecost vary in length depending on the date of Easter (see BCP, pp. 884-885).
Source: https://www.episcopalchurch.org/glossary/ordinary-time/