(1) To fill a data structure with bits or characters.  See 
padding.
(2) (PAD)  (
Packet 
Assembler/
Disassembler)  A communications device that formats outgoing data into packets of the required length for transmission in an X.25 packet switching network.  It also strips the data out of incoming packets.
(3) An iPad-like tablet.  See 
iPad and 
tablet.