The Nav2 planner is a Task Server in Nav2 that implements the nav2_behavior_tree::ComputePathToPose interface.
A planning module implementing the nav2_behavior_tree::ComputePathToPose interface is responsible for generating a feasible path given start and end robot poses. It loads a map of potential planner plugins to do the path generation in different user-defined situations.
See the Navigation Plugin list for a list of the currently known and available planner plugins.
See its Configuration Guide Page for additional parameter descriptions and a tutorial about writing planner plugins.