Relating to or denoting a light bulb which is designed so that its beam is focused automatically when it is fitted inside a lamp, especially a vehicle headlamp.
（尤指车前灯）预聚焦的，定焦距式的
Definition of prefocus in US English:
prefocus
adjectiveˌprēˈfōkəs
attributiveRelating to or denoting a light bulb which is designed so that its beam is focused automatically when it is fitted inside a lamp, especially a vehicle headlamp.