What are custom parameters?

The correct answer is Parameters that can be invoked in your SQL query and replaced by specified values during query execution because custom parameters are placeholders that can be defined within an AMC (Amazon Marketing Cloud) SQL query. When the query is executed, these parameters are replaced with specified values, allowing for more flexible and reusable queries. This approach enables users to dynamically modify certain parts of the query without having to hard-code specific values, making the queries more adaptable to different scenarios and easier to maintain. The other options, such as synthetic signals, credentials for S3 buckets, and custom models for lookalike audience generation, do not accurately describe the functionality of custom parameters in AMC.