What do we mean by Tracking In styling ? How we can implement Tracking w.r.t styling using xsl?

In few of the competitive xslt technical sessions I saw they use to mention a styling chart where they are mentioning while writing xslt make sure we are using the specification like

Tracking: -3
Kerning: Optical

Now I saw we have font-kerning: but that is limited to

font-kerning:auto|normal|none 

I don't see a option like optical and also not getting any fruitful information about tracking; so if any one can help me with the input how I can implement this Tracking and Kerning options in my .xslt that will be helpful.

Tracking is just a different term for letter spacing:

> In typography, letter spacing, character spacing or tracking is an optically consistent adjustment to the space between letters to change the visual density of a line or block of text.
> _{source: Wikipedia}

In XSL-FO the corresponding property is letter-spacing.

There is no FO property controlling kerning (font-kerning is a CSS property), but if the font you choose has kerning information and the formatter you use supports it the resulting output will show the characters properly spaced.
If you are using FOP, kerning can be enabled / disabled when you register the fonts; by default, it is enabled.