What do individual plan parameters mean?

Each plan comes with the following parameters:

• Credits: Credits measure your API usage. One credit equals 0.5MB of output data. For example, files up to 0.5MB use 1 credit, files between 0.5MB and 1MB use 2 credits, and so on.
• Rate Limit: The maximum number of conversions allowed per minute.
• Concurrency: The number of conversions that can run at the same time.
• Max Delay: The maximum time the converter will wait for asynchronous JavaScript to complete. This is separate from the overall conversion time limit of 60 seconds.