An Amazon OpenSearch is a successor to something you may have heard before called, Amazon ElasticSearch.
So the name change was due to some licensing issues.
So in DynamoDB, just to do a comparison, you can only query the data by primary key or if you have indexes on your database.
But with OpenSearch, you can actually, as the name indicates, search any fields, even for partial matches.
So it's very common to use OpenSearch to provide search to your application.
And so you would use OpenSearch as a compliment to another database.
So OpenSearch can be used for search, but also as the name doesn't indicate, you can also do analytic queries on top of OpenSearch.
You can use something called OpenSearch Dashboards to create visualizations on top of your OpenSearch Data.
So you have two modes to provision an OpenSearch Cluster, either you use the managed cluster option and then actual physical instances will be provisioned for you and you will see them, or you can go the serverless route and have a serverless cluster, where everything from scaling to operations is handled by AWS.
And OpenSearch has its own query language, it does not natively support SQL, but you can enable SQL compatibility via a plugin.
So you can ingest data from different places, such as Kinesis Data Firehose, IoT, CloudWatch Logs, or any of your custom-built application.
You have security provided through integration with Cognito, IAM, you get at rest encryption and in-flight encryption.