It can be helpful to report on student class attendances for a grading period. When pulling attendance data into a Class Enrollment query, you will see the fields to the right as options in the Attendance Section.
P1 is referring to the first “minor” grading period. P2 would be the second minor period, and so on. Similarly, T1 is referring to the first major grading period. You can see how your grading periods are configured (mid, minor, or major) via the Grading Periods query located in the Configuration section of the System Homepage.
You might also find these documentation articles helpful: