Three Rivers Press

Three Rivers Press is the trade paperback imprint of the Crown Publishing Group, a division of Random House. It publishes original paperback titles as well as paperback reprints of books issued initially in hardcover by the other Crown imprints.

From the Wikipedia article “Three Rivers Press”, licensed under CC BY-SA 4.0.

An imprint is a brand inside a larger publishing house, often with its own editors and list. Imprints of large groups usually acquire through literary agents; read recent titles to see whether your book fits the list, then target agents who sell to it.