From Longman Dictionary of Contemporary Englishby the wayby the wayAND/ALSOused when saying something that is not related to the main subject you were talking about before By the way, have you seen my keys anywhere? → way
Examples from the Corpus
by the way• By the way, we are ruling out places like South Bend, Ind.• Ni-cads, by the way, should not be left in a discharged state for very long periods.• Fast, by the way, is the operative word.• And it's Jonathan, by the way.• Davis is a man, by the way, not a monster.• Oh, by the way, Vicky called while you were out.• His narrating hero and anchorman, Nicholas Jenkins, is constantly being mildly surprised by the way things and people turn out.• You can tell that by the way they muck schedules about. 