Applications and websites which use Twitter are built using the Twitter API. When using an application built on the Twitter API, you may run into a situation where you are told you have been rate limited. What this means is the application you are using has tried to get information from Twitter too many times in the last hour.
This policy affects the Twitter APIs in different ways. To know what action to take you need to know what each API does:
The REST API is used by many applications to do things like post Tweets, follow someone, create lists and more.
The Search API is for performing searches, just as you would on Twitter.com.
The Streaming API is for application developers who want to receive a real-time stream of the public Tweets on Twitter.