Learner's definition of CB
[noncount]
: a range of radio frequencies that people and especially truck drivers use to talk to each other over short distances often while driving（卡车司机驾车时相互联系用的）无线电波段 —
often used before another noun常用于另一名词前 also : a radio that uses this range of frequencies民用无线电台 ◊ CB is an abbreviation of “citizens band.”*CB是citizens band的缩略词。