You are probably thinking of Google Custom Search Engine.
Google Custom Search enables you to create a search engine for your website, your blog, or a collection of websites. You can configure your search engine to search both web pages and images. You can fine-tune the ranking, customize the look and feel of the search results, and invite your friends or trusted users to help you build your custom search engine. ...
There are two main use cases for Custom Search - you can create a search engine that searches only the contents of one website (site search), or you can create one that focuses on a particular topic from multiple sites. You can use your expertise about a subject to tell Custom Search which websites to search, prioritize, or ignore. Because you know your users well, you can tailor the search engine to their interests.
I use a CSE for several hundred blogs that cover a particular topic of interest and it works great.