First my condolances on the passing of your wife.
RMD stands for required minimum distribution. It's the minimum amount of money you're required to take out of your retirement plan if you were 72 years old in 2023 or once you turn 73 in 2023.
Your 1099-R issuer is required to follow RMD rules and regulations, so if you received a distribution and you're at least 73 years young, you can be almost certain you received an RMD. Check with your plan administrator if you're still not sure. Chances are you will automatically receive RMD's from the issuer. If you do not have a lot in your IRA you won't see a significant change in income.