要塞是指險要的關隘，亦作要隘，常出現邊城或战略区域的要害處，是一種特别加固且固定的军事设施。

Defensive structure consisting of a barrier that can be employed for defense against attack

The term backline is used in popular music and sound reinforcement system contexts to refer to electronic audio amplification equipment and speaker enclosures that are placed behind the band or the rhythm section on stage, including amplifiers and speaker cabinets for guitars, bass guitars and keyboards.