From Wikipedia:
Google Trends is a public web facility of Google Inc., based on Google Search, that shows how often a particular search-term is entered relative to the total search-volume across various regions of the world, and in various languages. The horizontal axis of the main graph represents time (starting from 2004), and the vertical is how often a term is searched for relative to the total number of searches, globally.[1] Below the main graph, popularity is broken down by countries, regions, cities and language. Note that what Google calls “language”, however, does not display the relative results of searches in different languages for the same term(s). It only displays the relative combined search volumes from all countries that share a particular language (see “flowers” vs “fleurs”). It is possible to refine the main graph by region and time period. On August 5, 2008, Google launched Google Insights for Search, a more sophisticated and advanced service displaying search trends data. On September 27, 2012, Google merged Google Insights for Search into Google Trends.
A demo:
