APIs come in many shapes and sizes, all across the programming universe. They represent tools, packages, and more that developers can tap into to assist in their development work. In our case, we're interested in web APIs specifically -- access that is available to developers, often for free, enabling them to tap into the provider's data, tools, libraries, services and more. While there are typically terms and conditions of use, they nevertheless can provide incredible capacity to any developer's web work.
Many of the weather sites you've used, if not all, use APIs to get their data from weather-gathering services (often much fewer than the front ends that offer their information! Through maps, search engines, account access and more, you are using APIs all the time as web consumer. In this tutorial, we'll look at how to tie into one to make a search engine that returns book information in response to user queries!
The Goodreads API gives developers access to their entire database of book and author information, but also the social network of it's users. It can be used as a means of reading and submitting reviews (there are over 10 million reviews across the 700,000 titles and growing), and can also let members connect to their accounts!