while; when.
This conjunctive adverb expresses simultaneous action and is derived from sabu , "to coincide".
While you were sleeping, I went walking.
The children, while playing in the middle of the road, were nearly hit by the car; good now [it] was able to stop at once.
Her room was swept by her while her friend was not present.
She swept her room while her friend was not there.
The hot water was touched by him while [it] was boiling, [that] is the reason his hand burned.