Intercalation /(?)/

In·ter·ca·la·tion

Intercalation

n.
  1. The insertion of a day, or other portion of time, in a calendar. (Chron.)
  2. The insertion or introduction of anything among others, as the insertion of a phrase, line, or verse in a metrical composition; (Geol.)
    Intercalations of fresh-water species in some localities.