In the Digimon Adventure dub, known as simply 'Digimon' or 'Digimon: Digital Monsters', Piyomon's name has been changed to 'Biyomon', and Pyocomon's to 'Yokomon'. As far as I can tell, 'biyo' and 'yoko' have no real meaning - they're just strangely altered versions of the original names.
The names weren't the only things that were changed - Biyomon's personality seems to be slightly different than Piyomon's. While she's still really friendly and loves Sora and everyone else a lot, she's a lot less obsessive, and more focused and level-headed - she's kind of like a friendly and just superhero. In return, Sora never seemed to have a problem with her partner at all. In episode four, which focused on Sora and Piyomon's relationship, the dub versions of both characters acted quite different. Biyomon did not completely obsess over Sora - instead, she was simply eager to protect her as well as her other friends, and Sora didn't seem wary of Biyomon at all.
For instance: While walking through the desert in the fourth episode, Piyomon cheered Sora on and kept trying to converse with her, which caused Sora to ever-so-slightly snap at Piyomon. Piyomon responded by hanging her head, saying that she'd do as Sora wished. This made Sora feel bad, so she told her Digimon partner that she could keep on following her if she wanted to. Piyomon regained her happy mood immediately, running back up to Sora to express her undying love for her.
The dubbed version of this scene was completely different. Biyomon did not bother Sora - when she got to the part where she hung her head, she said she was tired, and could barely walk anymore. Sora suggested that they could all pretend it was raining, an idea that pleased Biyomon - she exclaimed her love for rain when she ran up to Sora.
In conclusion, it saddens me that American dubbers find it necessary make so many pointless little changes, but hey. Back when I was only able to watch the dub, Biyomon was still my favorite character, but when I got to watch the original series and discovered Piyomon's real personality, my love for her seriously increased. I generally dislike all dubs, and the very IDEA of dubbing, really (if you were to grow up with Bugs Bunny as Snurre Sprett, you'd understand) and try to avoid them whenever possible.