Lanefan
Victoria Rules
In days of old "campaign" usually meant something considerably bigger than a single string of related adventures. Such strings could certainly be embedded into a campaign, but most times a single string wasn't the whole game."Campaign" is the word WotC uses to describe their hardcover "long continuous adventure spanning many levels" D&D books.
"Adventure Path" I assume is a Pathfinder or perhaps 3E/4E term since I haven't seen it used on any WotC product since I returned to D&D in 2017 after a 20+ year break, and also was not a term I encountered prior to that break when playing from '86-'94. It has definitely never been used by WotC in the 5E era, and I can't recall it ever being used in the 1E or 2E eras, when we used the word "campaign" in the same way that 5E uses it.
Over time, "adventure path" informally became a useful term for this string-of-related-adventures idea within a campaign, and later, for a string of related adventures that was itself the whole campaign. Then Pathfinder came along and kinda stole that term for its own use, meaning WotC couldn't really use it anymore for competitive/marketing reasons. And so WotC have since been trying to co-opt the term "campaign" for their own purposes, which is rather annoying.