This lecture covers Conc-Tree Combiners, which are used in parallel programming in Scala. It explains how Conc Buffers append elements into an array, how Chunk Nodes store arrays of elements, and how the expand method inserts chunks into the Conc-tree. The lecture also details the combine method, which merges two Conc Buffers, and the result method, which packs chunk arrays into trees. A demo is shown using the Rond Bluffen benchmark, and the lecture concludes with a practical example of parallelized tasks in Scala.