Google API stands for ‘Application Programming Interface’. It is important to remember that all of Google’s APIs are only available in beta version, which means they are mostly still in their initial trial release.It's a software engineering term for a documented set of functions/methods/classes that developers can use to extend the functionality of an application.
for each apps of google there is seperate api for example google search engine has one google map has another and so on. using this api you can fetch result from google what the provide themself, may be not the same quality but not so bad either.