Pyom is an onomatopoeia word. It is the sound that it sounds like when read. Pyom, in this case is generally the sound of someone or something moving around or past an observer at a high velocity. It is the sound of anything coming towards you and instantly afterwards, moving away from you at an accelerated pace. This sound is accentuated by what we call the doppler effect. It starts at a high pitch and then as it goes by, turn to a lower pitch.
Think of a race car passing by you. Or a person on a motorcycle. Or someone coming into an online conversation and leaving very quickly thereafter.

Typical in Otaku Anime Network DC++ hubs:
Jackie: *sees AkkerKid coming from the horizon*
AkkerKid: *Pyoms by and leaves a bucket of cookies for everyone*
Jackie: OH COOKIES!!!
Jackie: I still didn't get to ask him if I could have a slot... pifflesticks...
by AkkerKid December 5, 2006
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