Noun:

1. an electronic device consisting of a rotatable ball in a housing; used to position the cursor and move images on a computer screen;

   "a trackball is essentially an upside-down mouse"
   

trackern.追踪者；跟踪器trackn.轨道；跑道；踪迹；小路；乐曲v.追踪；跟踪Track initial轨迹起始track vehicle履带式车track telling轨道辨别track bearing航迹角track carrier履带提架track joining接轨track renewal线路更新track tractor轨道牵引车track control线路值班员, 进路控制器tracking ship航天跟踪测量船, 跟踪遥控船