(of a day or a month) inserted in the calendar to harmonize it with the solar year, e.g. 29 February in leap years

eighteen months of twenty days each and five intercalary days

(of an academic year or period) additional to the standard course and taken at a different institution

the intercalary year is taken between the second and final years

(of the meristem of a plant) located between its daughter cells, especially (in a grass) at or near the base of a leaf