Tweaking refers to fine-tuning or adjusting a complex system, usually an electronic device. Tweaks are any small modifications intended to improve a system.
In electronics, it is a synonym for "trimming." Analog circuit boards often have small potentiometers or other components on them that are used to calibrate or adjust the board as a service procedure: the small insulated screwdriver used to turn them is often called a "tweaker."
This use was echoed in the name of the product Tweek, a popular but controversial audio product during the 1980s, which was claimed to improve the electrical characteristics of audio switch contacts.
Hardware tweaking is a process of modifying certain parts of a hardware such as changing the cables, cleaning the heads of a VHS player with a branded cleaning fluid or oiling the moving parts of an engine with the best possible oil.
Computer hardware 
Computer hardware tweaking is an extension of hardware tweaking, specifically geared towards the components of a PC. They include: changing voltage and clock rates of processing units, modifying RAM unit timing, improving cooling systems to reduce chance of overheating, etc.
Tweaks specifically designed to allow a processor to operate at a higher clock speed than normal are known as overclocking.
Software tweaking is the process of improving the performance of an application or the quality of its output. There can be two ways of accomplishing this: manually (that is, if one is familiar with programming; though it may be irrelevant if the source of the application is closed, and there are no built-in means to adjust its performance) or using another piece of software specialized for that purpose (such as Red Button and SysTool, semi-automatic tweaking utilities used to improve the performance of Microsoft Windows XP. Tweaking of this kind generally increases usability, in terms of personal configuration preferences, rather than objective performance of the system overall).
Some very precise applications need constant and thorough tweaking to stay up to date and deliver best possible results. One of the most obvious examples of such a fine tuning is LAME MP3 encoder, whose 3.9x branch is not only considered as the state-of-the-art MP3 encoder, but also continues to shape the boundaries of the MP3 codec and stay competitive with its successors.
See also 
- "SysTool - System Tweaking and Overclocking Utility". techPowerUp!. Retrieved 2007-06-19.
- "LAME". Hydrogen Audio Wiki. Retrieved 2007-06-27.
- Roberto Amorim; Sebastien Mares (2005). "Results of Public, Multiformat Listening Test @ 128 kbit/s". Retrieved 2007-06-27.
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- Tweakguides.com Site with various Windows and PC Game tweak guides