Corrective Distribution of Excess Contributions
Generally, if the contributions made for you during the year to certain retirement plans exceed certain limits, the excess can be corrected. The excess is distributed to you by the plan (along with any income earned on the excess).
If your retirement plan made a corrective distribution of excess amounts (excess deferrals, excess contributions, or excess annual additions), your Form 1099R should have the code "8," "B," "P," or "E" in box 7.
This information is found in Publication 575, Pension and Annuity Income.