Yesterday a federal district court granted President Trump's request for a special master to review material seized from his Mar-a-Lago estate, and the court also temporarily enjoined the Government "from further review and use of any of the materials seized from Plaintiff's residence on August 8, for criminal investigative purposes" (page 23). The ground for all of this, the court said, was its "equitable jurisdiction and inherent supervisory authority" (page 1). The claim to inherent supervisory authority seems improbable to me. Whatever that authority is, and it is debated, I will leave that aside to consider the court's "equitable jurisdiction."
"Equitable jurisdiction" means the power of a court of equity to act. It's not quite the same as subject-matter jurisdiction, though the concepts overlap. We could say "you have subject-matter jurisdiction under x statute, but you don't have equitable jurisdiction because there is an adequate remedy at law." Equitable jurisdiction is required for equitable intervention.
