PLS is a computer file format that stores multimedia playlists. It is a more expressive format than basic M3 U, as it can store (cache) information on the song title and length -- extended M3U supports this, too. However, M3U playlists, because of their simplicity, can be easily created with a scripting language such as Apple Script or Java Script, or even by hand.
PLS is a syntactic subclass of TFNP. A instance of PLS can be given in terms of polynomial algorithms that determine an exponentially sized graph. Given an input x and a vertex in the graph, the polynomial algorithms can compute the neighbors of the vertex in the graph and the cost of the vertex in the graph.