Practical definition: Political promises
In Jared Diamond’s excellent book Guns, Germs, and Steel poses a question via the mouth of a Papuan native: “Why do you have so much cargo?”
“Cargo” is a native word for ‘stuff,’ as in the kinds of goods commonly produced by an advanced society. Every primitive culture that has come into contact with an advanced civilization for the first time has shared an understandable awe at the explorer’s (or invader’s) ‘cargo’–from their explosive armaments down to their metal shoe buckles.
Now, a civilized person might assume that natives faced with ‘cargo’ might try to understand how it was made so they might begin to build approximations of it. But that would reflect the civilized person’s naivete. In fact, primitive people commonly endow things with a mystical property that goes beyond its form or function. For them, everything is guided by a higher spirit, a spirit may send the cargo their way versus toward someone else.
Down that mystical path, natives will begin engaging their existing theories about what moves the spirits, and begin to exhibit what, to us, looks like strange behavior to persuade the spirits to drive cargo their way. This is called a cargo cult.
Civilized people look upon cargo cults with a sense of wonder and amusement. We shake out heads at shirtless people dancing and praying to their version of Gaia, as if that might somehow make a washing machine appear. Civilized people would never do that.