OASDI stands for old age, survivors, and disability insurance, otherwise known as Social Security. Social Security tax may be deducted from your income but it is not a deduction on your tax return. If you work for a state or local government agency and are covered only by your state or local pension, you don't pay Social Security taxes so you won't see an amount in box 4 of your W-2. There are other individuals who are exempt from paying Social Security tax as discussed here: Who
Is Exempt from Paying Social Security Tax?