On box 13 of my W2 I have a x under retirement plan . what does it mean ?

[FrankF1]

A checkbox in Box 13 for your W-2 means that you were considered an "active participant" for any part of the year in a retirement plan such as a 401(k), 403(b), IRA-SEP, SIMPLE or plan for Federal, State or Local government employees.

You can contact your plan administrator for more information and details regarding participation in your employer's retirement plan.