You probably heard this in an advertising message for Kentucky Fried Chicken, which has long maintained that "a secret blend of 11 herbs and spices" gives the chicken its unique flavor. There are many herbs and spices available for seasoning food. Check your grocery store's cooking and baking aisle.
That is referring to the KFC Restaurant's 'signature recipe', which features eleven herbs and spices that are completely secret, and only known by the heads of the company. People have tried to discover what they are, but no one has definitely succeeded.