What is the meaning of pb?

noun

• A soft heavy toxic malleable metallic element; bluish white when freshly cut but tarnishes readily to dull grey.
  • usage: "the children were playing with lead soldiers"
  • synonyms: lead, atomic number 82
• A unit of information equal to 1000 terabits or 10^15 bits.
  • synonyms: petabit, Pbit
• A unit of information equal to 1000 terabytes or 10^15 bytes.
  • synonyms: petabyte
• A unit of information equal to 1024 tebibytes or 2^50 bytes.
  • synonyms: petabyte, pebibyte, PiB