PCD - Is Payload Correction Data. PDA - Is a Portable Digital Assistant. A PDA is smaller than a laptop and does not have a keyboard built in like a palmtop. PDAs are typically used for sending or receiving emails, taking notes or storing addresses. Many palm devices provide a cradle or infrared device to hotsync or beam information to a desktop system.
Some models come equipped with cellular-links or satellite links.
PDB - Is a Project Database. PDL - Refers to a Push Down List or Propositional Dynamic Logic. It is also a force equal to 0.1382 newtons. PDU - See Protocol Data Unit. Perigee - Is the point in a satellite's orbit where it is closest to its body of rotation.