Deprecated means, generally, that something is acknowledged but discouraged.
In IT, deprecation means that although something is available or allowed, it is not recommended or that, in the case where something must be used, to say it is deprecated means that its failings are recognized. The term may be used with almost any element of IT, including software, hardware, methods, models and practices.
In computer programming, a deprecated language entity is one that is tolerated or supported but not recommended. For example, a number of elements and attributes are deprecated in HTML 4.0 , meaning that other means of accomplishing the task are preferred. Many deprecated features became obsolete in HTML5, although browsers that support the features may continue to support them. In the Java programming language, a particular method may be deprecated for a given class of objects.
Even general approaches to something can be deprecated. Security through obscurity, for example, is an approach that relies on keeping coding and its potential vulnerabilities hidden, so that flaws are less likely to be detected and exploited. That model, and others such as security through minority and security through obsolescence, are deprecated in favor of security by design, which involves creating systems that are as secure as possible in the first place.