[font=trebuchet ms]The name "flanger" comes from something that was discovered back in the day of reel-to-reel analogue tape recording. If you drag your fingers lightly on the flange of the feed reel during mix-down, you can cause just enough time-shift between tracks to cancel, or at least attenuate, some of the frequecy spectrum. This creates a thin, hollow kind of sound. Something like the #2 and #4 pickup selector positions on a Strat, but more extreme. And because the tape reel does not drag smoothly, the depth of this effect tends to change over time.

Modern effects units simulate this effect by mixing the 'dry' signal with a slightly delayed copy. The amount of delay is changed slowly, adding a swept 'aw' sound to the effect. It's a distinctive sound. Picked notes tend to go 'doink' instead of 'ping'. It's easy to recognise, once you've identified it.

'Phasing' is similar, but it adds a softer, 'whoosh' kind of sweep to the track.[/font]