Azure Cosmos DB Concept

Some of the concepts in Azure Cosmos DB:

• Database account is a container for one or more Azure Cosmos DB databases.
• Database is a container for one or more collections
• Collections are like tables in relational databases without a schema. A collection contains documents.
• Documents are an unstructured set of key/value pairs, read and written in JSON format. They are the logical unit and which is roughly equivalent to a relational row. Documents of similar types are organized into collections.
• Partitioning is the distribution and grouping of your data across the underlying resources.
• Index is a catalog of document properties and their values. 
• Request Units (RUs) measures the throughput at which rate data is processed. RU is the amount of CPU, disk I/O, and memory required to read 1 KB of data in 1 second.

Additional insights can be found at How To Design And Query Data In Cosmos DB (c-sharpcorner.com)