Simple and SEP-IRAs are two different types of IRAs with somewhat different rules. Look at this link for a brief discussion by the IRS on these retirement accounts.
Normally, each of these are part of a small business. If you never worked for a small business (less than 100 employees), you probably don't have either one, but just a regular IRA.
You should be able to call the administrator who sent you the 1099-R and just ask what type you have.