***Not a teacher***
An RSS feed is something you can subscribe to on a web page. Normally it will be on a page containing a blog, news articles or something else that changes frequently. The idea is that every time the web page is updated, you receive a notification (often by email) with the updated content. The advantage of this is that you can maintain a group of RSS feeds which effectively 'keep an eye on' multiple web pages, and thus avoids you having to check them regularly to see if there has been any change.
Lots of detail on RSS - Wikipedia, the free encyclopedia
The RSS feed icon is:
I assume 'social feeds' refers to RSS feeds on social networking type sites - twitter etc.