This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
An intent can be compared to a software signal that your application raises so as to communicate its interest to the Operating system/Android Runtime. The system then builds a list of all the parties that have registered themselves for this signal. The best match is chosen to cater to the request and in case of multiple matches user is given a choice.
For example, if my application wishes to view/open a picture it will raise a intent for ACTION_VIEW and pass appropriate data in intent argument, so that the party intercepting or responding to this intent can identify the image to be displayed an take appropriate action.