An API is one way a company lets other people access their data or services.
Here are three examples of APIs:
Google - Search API
Given a search term, this API will give you back a list of search results.
Alchemy - Sentiment Analysis API
Given text, this API will tell you whether it has a positive or negative sentiment.
Uber - Request a Ride
Given a location, this API will request an Uber ride.
In the past, APIs have mostly been used by software engineers to have computers talk to each other. Blockspring changes this. The Blockspring plugin lets you use an API from a spreadsheet.
See these examples of how APIs can be used from a spreadsheet with Blockspring.