The REAL ID Act of 2005 established security standards for the issuance of identifiction documents, and prohibited federal agencies from accepting those documents that did not adhere to the Act. It has been up to the individual states to issue driver licenses and identification that comply with the Act. Many have not done so.
On July 1, 2019 the State of Tennessee will begin issuing driver licenses and identification cards that comply with the Real ID act. So you may ask yourself, do I need a new ID?
Beginning October 1, 2020 everyone must have an ID that complies with the REAL ID Act to access federal buildings that require ID (including military bases), and board U.S. domestic flights, among other things. If you do not obtain a compliant ID before that time you will not be allowed entry. Without a valid ID you will not be allowed entry to an airport's secure area by the Transportation Security Administration (TSA).
Without a REAL ID, you will otherwise still be able to drive in Tennessee, and your ID will be valid for state-level purposes. You will not need a REAL ID compliant driver license or ID card to vote, purchase alcohol or cigarettes, access hospitals, visit the post office, access federal court, or apply for and receive federal benefits such as social security or veteran's benefits.