A Transformative Agreement (TA) is a set of terms negotiated in a license between a publisher and a library, library system/consortia, or national organization, which is fundamentally designed to shift costs away from subscription-based reading and toward open access publishing. While there is a long road ahead, a TA is transitional in that the purpose is to eventually shift costs to publishing and eliminate subscription-based reading access to scholarly research.
More about Transformative Agreements at the McDermott Library can be found here.