engaged d tone占线音
distinctive engaged tone detail小交换机特殊忙音
ET Engaged Tone占线音
N-COUNT（可数名词） If you try to make a telephone call and get an engaged tone, it means that you cannot make the call because the line is already being used by someone else. (电话的)占线音; 忙音
I tried the number again, got an engaged tone.
我又拨了一次那个号码，电话还是占线。