4 ms·Etymology: they sound like squealing pigs during operation.by block_dagger 3y agoEtymology: they sound like squealing pigs during operation.stavros 3y agoPipeline Inspection Gauges, or PIGs.decafbad 3y agoYes, it's called backronym.yreg 3y agoIn my language this is called moleing (from mole).