SPARK TUNING TERMS
IAT Sensor
The intake air temperature sensor tells us the how hot the air is as it enters the engine. The higher the temp, the higher the chances of knock. If intake temps can be lowered, more ignition-timing advance can be added, which adds power (unless you've hit MBT, which is unlikely under a high load). This ability to add advance when temps are lowered are part of the reason why cold-air intakes and intercoolers can add power.
Detonation
Detonation, or knock, is when the air/fuel mixture ignites before the cylinder reaches maximum pressure. The result is a supersonic and out of control explosion in the chamber that puts stress on the engine that it wasn't designed for. Low-octane fuel, high compression ratios, advanced ignition timing, high intake temps, and a number of other things can cause detonation. Detonation breaks pistons and bends rods.
Preignition
This is when the mixture ignites before the spark plug fires. It is caused when isolated spots in the combustion chamber glow red-hot and ignite the mixture before it's supposed to. These hotspots can be caused by carbon build up, poor design, or other factors. Preignition isn't the same as detonation or knock. Anyone who's been in a junker that keeps running after it's been shut off knows what preignition is.
Electronic Timing Controllers
This is the way to go. On the low end of the scale are devices that simply retard the timing according to load. On the high end, we have the programmable ECUs that, just like tuning the fuel, allow us to make changes at any point of the map we encounter knock, leaving the rest alone. With the lower end types, you may have to retard the timing for the whole RPM map, even though it may only knock at 4500 RPM.
Base Timing Adjustment
This is the ghetto way to adjust the timing. This is usually done when an owner makes mods but doesn't realize that they need ignition mods until they hear that ugly metallic ping of detonation. While this may ward off knock the 10 percent of the time the cars at full throttle, the other 90 percent of the time it'll be a sluggish piece of crap. Many low-end and backyard turbo "kits" utilize this to avoid detonation under boost. People that add high-compression pistons and have no form of spark control often resort to this level of barbarianism, too.
Knock Sensor
A knock sensor is a device that measures engine noise and sends a signal to the computer when there is detonation. Most sensors have some "background" noise in their signals, but real knock events are easily distinguished because they are so violent and register big values when it happens.