during; throughout; all through
Used after a noun expressing a period of time to mean 'throughout that entire period' or 'all during that time'.
I swam in the sea every day throughout the summer vacation.
I kept looking outside the whole class.
He didn't say a single word during the entire meeting.
It kept raining the whole time we were on the trip.
中 (ちゅう) as a suffix just marks 'during' a period, whereas 間中 (あいだじゅう) is more emphatic that the action or state spans the whole period.
Standard kanji spelling; high news frequency.
Mixed kana-kanji spelling; less common but still encountered.
Compound of 間 (あいだ, 'interval, period') and 中 (じゅう, 'throughout'). The reading じゅう is a rendaku form of ちゅう.