The main components of ROS are:
1. ROS Master: This is the main controlling node that coordinates communication between other nodes in the ROS system. It is responsible for keeping track of all the topics and services available in the system. Example: roscore
2. ROS Nodes: These are independent processes that communicate with each other using ROS topics and services. Examples: robot_state_publisher, move_base, and rviz
3. ROS Topics: These are the channels through which nodes communicate with each other. They are used to publish data and subscribe to data. Examples: /cmd_vel, /odom, and /tf
4. ROS Services: These are request/response communication methods between nodes. They are used for synchronous communication between nodes. Examples: /gazebo/spawn_urdf_model and /gazebo/delete_model
5. ROS Messages: These are the data structures exchanged between nodes. They are used to define the format of the data that is sent and received. Examples: std_msgs/String and geometry_msgs/Twist