while; during; in the middle of
Describes an action or state that occurs at the peak or middle of another activity or period.
Use 最中に to say that something happens right in the middle of another ongoing action or event, emphasizing that the other activity is at its peak. It often carries a nuance of interruption or an unexpected event occurring while you are busy doing something. For example, you might say you received a phone call while you were in the middle of eating. The pattern is slightly formal and more common in written Japanese or in polite conversation, but it's perfectly acceptable in everyday speech.