Starter Stats are the Stats a Character has once Character Creation is finished. This includes any changes to Stats made during Step 3 of Character Creation.
Starter Stats are used to determine how much Experience is used to gain a rank in a Stat. See Ranking Up for more details.
Starter Stats only change when explicitly stated in rules such as but not limited to those found in Cyberware or Masteries.
Example: Miles the Human begins Character Creation with a 5 in Agility and Brawn from being a Human. Miles increases his Agility by 2 and decreases his Brawn by 1 as part of Step 3. Miles the Human Ace finishes Character Creation with an Agility of 7 and a Brawn of 4, these are now his Starting Agility and Starting Brawn.