AT stands for Advanced Technology. In general term, Advanced Technology can be used to refer High Technology.
In the computer world, the technologies which are incorporated in advance computer electronics, referred as advance technology. However, there is no specific class of technology that can be called as advance technology because the definition shifts and evolves over time. For example: the products which are so hyped as advance in the past may now be considered to be everyday or outdated technology.
Generally, the term High Technology (high-tech) is preferred over advance technology. Many gadgets having the latest features are considered as high-tech gadgets.
There are so many fields which uses advance technology. For example: