n. A subsection of the day during which a TV or radio program, or a series of related programs, airs.
Thinking in terms of radio rather than music means programming according to what people are doing during the day — using 'dayparts' — such as morning drive and midday office listening.
CBS Television Network President James H. Rosenfield says that network 'has no plans to change its advertising standards' for children's programming… 'CBS does not believe there is anything wrong or unfair with truthful advertising on television. This applies to all dayparts, including Saturday morning.'
This word will be ancient history to anyone who has worked with television or radio scheduling, because daypart has been part of scheduling jargon for probably a quarter of a century or more. What interested me in the word was reading an article on Internet advertising and seeing daypart used without explanation, as though the reader should, after all, be familiar with such a term. It wasn't hard to figure it out from the context, but I wanted to see if the word was being used casually in non-industry publications. What I found was that, yes, the media quite often used the word without so much as a how-do-you-do. However, the majority of cites fell into one of two camps — using the word with an explanation or an example (as in the first citation), or including the word as part of a quotation from someone in the industry, as seen in the earliest citation.