noun which may take the genitive case particle 'no'
busy (phone); engaged (line)
Polite expression used mainly in telephone contexts to indicate the line is busy. Often seen in phrases like お話中です or お話中でつながらない.
See also: 話し中
When I called, the line was busy.
It's busy and I can't get through.
I'm sorry, Tanaka is on another line right now.
No matter how many times I call, I can't get through because the line is busy.