Over at the Travel SE beta (it's in private beta so I'm not sure how many here will be able to access it), I came across a question whether the OP uses "clearance through US Customs" when I'm assuming s/he actually means US immigration. (Here, I'm relying on the definition that 'immigration' handles visa clearance, 'customs' handles tax collection for goods.) I have come across this particular usage earlier too, mostly among American travellers. Is this usage US-specific - and is it an 'error'*?
(* An error in the sense that the actual department at the airport, say, is US Immigration but people mistakenly call it 'Customs'.)