From GameBrew - a wiki dedicated to Video Game Homebrew.
Pseudo-emulates the PS1 BIOS in 3D on the 3DS! Remember! This cannot run games, so you're only limited to the BIOS.
Q: What's a pseudo-emulator?
A: An app that gives the impression of it being an emulator, but actually isn't. In PDSX 3D's case, it may look like it's emulating the BIOS of the PS1 on the 3DS or 2DS console, but it's actually a near-faithful recreation/mimic of it, including the logo and menu screens (as you'll see in the source code).