FICA is short for Federal Insurance Contribution Act. Check your pay stub from work and if you see this tax taken out of your check, know that this tax goes to the Social Security Administration to fund the Social Security Retirement, Disability and Medicine programs.
If you worked “for cash” do not expect to receive any social security disability or retirement money. If everyone else is paying taxes and “pilling up” funds for possible disability or retirement, you are spending your money each week. You are eligible for nothing. Frankly, if you are working “for cash” stop immediately and find a “legal job”.