The amount of data that can be processed or transmitted in a given time period. Like the number of cars that can pass through a tunnel per hour.
A database with high throughput can process thousands of transactions per second during peak shopping periods.
Throughput is a performance metric (not a single cloud service). All major cloud providers expose throughput in their networking, storage, database, and messaging services via service limits, instance sizing, and monitoring metrics (for example: network bandwidth, IOPS/MBps, requests per second, or messages per second).