When something is said to be deprecated, what does it mean?
Answer:
In programming world, a feature or a function is marked as deprecated when there is a newer feature or function that replaces the deprecated one.
The users are usually made known of that deprecation by either showing the deprecated information in the documentation or by triggering a deprecated notice or warning when the deprecated function is called.
Deprecation process gives programmers time to update their code by replacing their code that uses the deprecated items with the new one that supersedes it.
Sample deprecated features in PHP 5.3.x: http://php.net/manual/en/migration53.deprecated.php