refers to the various multiple hour segments of televisions 24 hour broadcast day. Dayparts are typically segmented as follows: 6a - 9a Early Morning 9a - 12n Morning 12n - 4p Daytime 4p - 6p Early Fringe 6p - 7p Early News 7p - 8p Prime Access 8p - 11p Prime 11p - 11:30p Late News 11:30p - 1a Late Fringe 1a - 6a Late Night
A daypart is a section of the viewing day, for example Breakfast (0600-0924) or peak time (for which there are various definitions).
Broadcast time period (segment), eg daytime 10:00am to 4:00pm. Often applied to segments which are used by TV companies in allocating rates to different parts of the day - but there are no generally agreed exact definitions by time period.