Parameters are the publicly visible configuration settings of a data source. You can freely read and change them, as opposed to credentials.
For example, for the PostgreSQL plugin, the host and the port are the parameters. In case of a SaaS like Stripe, the account ID is a parameter.
Parameters cannot be reused across data sources.
Some plugins allow you to configure parameters for a specific table that the plugin provides. For example, if you're adding an S3 bucket of CSV files to Splitgraph and making a repository with each table pointing to a different CSV file, the file name will be one of the table parameters.