MATLAB is a high-level language and interactive programming environment for numerical computation and visualization developed by MathWorks. MATLAB can be used when performing tasks such as signal processing and communications, image and video processing, computational finance, and computational biology. It is the foundation for a number of other tools, including Simulink and various toolboxes that extend its core capabilities.
Some informative links that show up quite often in answers:
- MATLAB documentation for the most recent version (R2012b)
- Archived documentation for prior versions (NOTE: only available to licensed users)
- MATLAB Central File Exchange: a repository of user-contributed MATLAB tools
- MATLAB Central blogs: usually updated weekly by a number of MathWorks employees
- Undocumented MATLAB: "Charting MATLAB’s unsupported hidden underbelly"
- MATLAB Answers: a collaborative environment for getting answers to questions about MathWorks products, similar to Stack Overflow
- comp.soft-sys.matlab Usenet group: can be accessed online through the MATLAB Central Newsreader hosted by MathWorks, or using Google Groups
- MATLAB Cody™ is a place where you can go to find a variety of Matlab based coding challenges that will help to expand your understanding of Matlab.
- MATLAB Wikipedia Article
See also here for a meta discussion about the MATLAB tag on M.SE.