Commonly used messages in ROS. Includes messages for actions (actionlib_msgs), diagnostics (diagnostic_msgs), geometric primitives (geometry_msgs), robot navigation (nav_msgs), and common sensors (sensor_msgs), such as laser range finders, cameras, point clouds.
See here: https://github.com/ros/common_msgs/blob/ef18af000759bf15c7ea036356dbdce631c75577/trajectory_msgs/msg/MultiDOFJointTrajectoryPoint.msg#L8
Not a huge deal, since the contents are essentially the same (6 doubles) but I would expect to see a definition using geometry_msgs/Accel: