It is a centralized store to manage your configuration data, whether plain-text data such as database strings or secrets such as passwords. This allows you to separate your secrets and configuration data from your code.
Parameters can be tagged and organized into hierarchies, helping you manage parameters more easily.
Systems Manager is integrated with AWS Key Management Service (KMS), allowing you to automatically encrypt the data you store.
You can also control user and resource access to parameters using AWS Identity and Access Management (IAM)
AWS Secrets Manager
AWS Secrets Manager was tailored specifically for secrets, so it is similar to the Parameter store, but with these differences:
It is not limited by the number of parameters allowed (currently 10000)