The percentage of I/O credits remaining in the burst bucket of your RDS database. This metric is available for basic monitoring only.
To find the instance sizes that support this metric, see the instance sizes with an asterisk (*) in the EBS optimized by default table (https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ebs-optimized.html#current) in Amazon RDS User Guide for Linux Instances.