According to the General instructions:
" Memorials During Privileged Seasons
On Sundays, solemnities, and feasts, on Ash Wednesday, during Holy Week, and during the octave of Easter, memorials that happen to fall on these days are disregarded.
On the weekdays from 17 to 24 December, during the octave of Christmas, and on the weekdays of Lent, no obligatory memorials are celebrated, even in particular calendars. When any happen to fall during Lent in a given year, they are treated as optional memorials.
During privileged seasons, if it is desired to celebrate the office of a saint on a day assigned to his or her memorial:
a. in the office of readings, after the patristic reading (with its responsory) from the Proper of Seasons, a proper reading about the saint (with its responsory) may follow, with the concluding prayer of the saint;
b. at morning prayer and evening prayer, the ending of the concluding prayer may be omitted and the saint’s antiphon (from the proper or common) and prayer may be added."
How does this exactly work? What is a “privileged season?”