a person or thing that traces something or by which something may be traced, in particular 追踪者,追踪装置,尤指 ■a bullet or shell whose course is made visible in flight by a trail of flames or smoke, used to assist in aiming 曳光弹 ■a substance introduced into a biological organism or other system so that its subsequent distribution may be readily followed from its colour, fluorescence, radioactivity, or other distinctive property 示踪剂,显光剂 ■a device which transmits a signal and so can be located when attached to a moving vehicle or other object 跟踪器(安装在移动车辆上或其他物体上,通过其发出的信号进行跟踪)