Refers to the period of daylight; can be used as a noun or adverbially. Similar to 昼間 (ひるま), but 昼中 may emphasize the middle of the day or be used in certain regional or stylistic contexts.
See also: 昼間
It's hot during the day, so I don't want to go outside.
He slept all through the daytime.
Compound of 昼 (ひる, 'daytime') and 中 (なか, 'middle'). The exact historical derivation is uncertain, but the word literally means 'mid-day' or 'during the day'.