Microelectromechanical systems (MEMS) are tiny devices capable of sensing or manipulating physical phenomena, with components typically ranging from 10 to 100 micrometers. The document discusses the history, fabrication methods, applications, advantages, and challenges of MEMS, highlighting their critical role in modern technology, including automotive applications. Key fabrication techniques mentioned include bulk micromachining and LIGA, which enable the production of high-performance MEMS devices.