A transmission method and apparatus, a priority definition method and apparatus, and a terminal are provided. The transmission method applicable to a communication device includes: determining target transmission when a target resource and a first resource at least partially overlap, meet a collision condition, or meet a multiplexing condition, where the target resource is related to a sidelink SL, the target resource has or does not have a first Uu priority, the first resource has or does not have a second Uu priority, and the first Uu priority of the target resource includes a Uu priority of the target resource and/or a Uu priority of at least part of information corresponding to the target resource.