Only your employer can tell you. It could be an HSA (health savings account). An HSA is a savings account that goes along with an HDHP insurance plan. But it could be something else. And if you do have an HSA and it is not recorded in box 12 with code W, then turbotax won't prepare your return correctly and the IRS won't be able to match your return with your W-2 and will probably send a letter of inquiry. You should try and get clarification from your employer before filing.
