An API, or application programming interface, is a set of rules that lets one software system request data or trigger actions in another. It defines what can be asked, how the request must be formatted and what the response will look like, so systems built by different vendors can work together.
Most modern business APIs are web APIs. One system sends an HTTP request to a specific address, called an endpoint, often including an access key or token to prove who is asking. The other system returns data, commonly in JSON format, or carries out an action such as creating an order. Requests typically read, create, update or delete records.
In retail and hospitality, APIs connect point of sale with ecommerce stores, inventory, accounting, loyalty and payment systems. For example, a website can ask the POS for current stock, or a new online order can be pushed into the store system for fulfilment.
Things to consider include authentication and security, rate limits that cap how many calls are allowed, documentation quality, and versioning, since a vendor may change or retire an endpoint. Poor error handling is a common pitfall: if a call fails and nothing retries or alerts anyone, data quietly drifts out of sync. Access keys should be stored securely and given only the permissions needed.
APIs matter because they replace manual re-keying and spreadsheet transfers with reliable automated data flow. The quality of a vendor's API often determines how easily a platform can be integrated into the rest of a retailer's technology.