The concept of RMD is that if you have a retirement account like a 401k or an IRA, you can't keep it tax-free forever, you have to withdraw something each year and pay the tax. How much you must withdraw is called your RMD (required minimum distribution) and is based on your age and the account balance at the end of last year.
However, because the payments on a traditional monthly pension are already based on your life expectancy, the entire amount counts as the RMD. Turbotax only needs to ask the question because the program can't tell whether a 1099-R is from a pension or an IRA.
If you have a pension, say the entire amount is the RMD.
If you have another retirement account, your broker can tell you what your RMD is. It is not a special withdrawal, just the total amount you must withdraw. For example, if your RMD is $5000, and you withdraw $1000 per month for living expenses ($12,000 per year), then you already withdrew more than the RMD. $5000 of the withdrawal was the RMD and the other $7000 was not.
