Application Programming Interface - a way for different software applications to communicate with each other. Like a waiter who takes your order and brings food from the kitchen.
When you check the weather on your phone, the weather app uses an API to get current weather data from a weather service.
An API (Application Programming Interface) is a general software concept, not a single cloud service. All major cloud providers expose APIs for their services (e.g., to create storage buckets, deploy apps, or manage databases). Providers also offer API management products to publish, secure, monitor, and monetize APIs.