Artificial Intelligence (AI) refers to the simulation of human intelligence in machines that are programmed to think like humans and mimic their actions. It is a branch of computer science aiming to create intelligent agents, where an intelligent agent is a system that perceives its environment and takes actions that maximize its chances of successfully achieving its goals.

AI systems are categorized into two main types:

1. Narrow AI: Also known as Weak AI, this type of AI excels at performing a specific task or a limited set of tasks. It operates under a limited pre-defined range or set of constraints. Most AI systems in use today are narrow AI, designed and trained for a specific task, such as voice recognition or image analysis.
2. General AI: Also known as Strong AI or AGI (Artificial General Intelligence), this type of AI would have all the intelligence and reasoning capabilities of a human being. It could understand, learn, and apply knowledge in different domains, reason through problems, have consciousness, and even possess emotional understanding. As of now, AGI remains a largely theoretical concept and has not been realized.

AI technologies use various methods such as machine learning, neural networks, deep learning, natural language processing, and robotics to achieve these capabilities. Applications of AI are vast and growing, including areas like healthcare, finance, transportation, entertainment, and more.

The development of AI continues to raise both excitement and concern, with ongoing discussions about ethical considerations, potential job displacement, bias in algorithms, and the societal impacts of highly intelligent machines.