These are the verbosity levels used by rosconsole and rospy/Overview/Logging

DEBUG

• Information that you never need to see if the system is working properly. Examples:
  • "Received a message on topic X from caller Y"
  • "Sent 20 bytes on socket 9".

INFO

• Small amounts of information that may be useful to a user. Examples:
  • "Node initialized"
  • "Advertised on topic X with message type Y"
  • "New subscriber to topic X: Y"

WARN

• Information that the user may find alarming, and may affect the output of the application, but is part of the expected working of the system. Examples:

  • "Could not load configuration file from <path>. Using defaults."

ERROR

• Something serious (but recoverable) has gone wrong. Examples:
  • "Haven't received an update on topic X for 10 seconds. Stopping robot until X continues broadcasting."
  • "Received unexpected NaN value in transform X. Skipping..."

FATAL

• Something unrecoverable has happened. Examples:
  • "Motors have caught fire!"