during
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.”
Always followed by a noun or noun phrase; it cannot be followed by a clause with a subject and verb.
during vs for — During marks the point in time when an event occurs; for measures the total length of time that event lasts.
during vs while — During precedes a noun phrase, while while introduces a clause with a subject and a verb.
During is a preposition and must be followed by a noun; use 'while' to connect to a clause with a subject and verb.
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.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.