PDA definition - a PDA is a Personal Digital Assistant. A PDA is a small digital device that is used to store information such as phone numbers, addresses, schedules, calendars, etc. A PDA may also be referred to as a handheld device or as a Palm. The Palm Pilot was one of the original PDA's and is now joined by others such as Palm Tungsten, HP IPaq, Palm Zire and the Toshiba Pocket PC.