during
prep.prep. at some point within a period of time. You use it to say that something happened while another event was going on.
prep. throughout the entire course or duration of a period; alternatively, at some point within the limits of a specified time or event.
It rained heavily during the night.
The students are not allowed to use their mobile phones during the final exam.
While the economy struggled during the initial transition period, the subsequent decade saw a remarkable recovery driven by technological innovation and increased foreign investment.
From Middle English during, durynge, durinde, durand, durende, present participle of duren (“to last”), equivalent to dure + -ing. Compare Dutch gedurende (“during”). More at dure.
Always followed by a noun or noun phrase; it cannot be followed by a clause with a subject and verb.
during I was sleepingwhile I was sleepingDuring is a preposition and must be followed by a noun; use 'while' to connect to a clause with a subject and verb.