ASIC - Application Specific Integrated Circuit
An Application Specific Integrated Circuit is an IC designed for a specific purpose than a general one. For example, a chip designed for a specific line of cell phones, may not work with any other type of cellphone, of same or different company.
The opposite of ASIC is a general purpose IC, such as a logic gate or a microprocessor in your PC, which can be used in a wide range of products and applications. Modern ASICs often include the entire microprocessors, RAM, ROM, flash memory etc.
As compared to a programmable logic device or a general purpose IC, an ASIC can improve speed, as it is designed for a specific purpose. ASICs are used in a wide-range of applications, including cell phones, PDAs, environmental monitoring system etc.
ASICs can be made by connecting existing circuit building blocks in new ways. Since these building blocks already exists, it is much cheaper to build a new ASIC rather than building a new chip from scratch.