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.