Tracking adds space, measured in points, between all the characters in a Text layer. A value of 0 sets the tracking to the system default value.
A positive value increases the spacing between characters, while a negative value brings the characters closer together.
The effect of tracking resembles that of the Kerning modifier, but it maintains equal space between characters for consistency, rather than changing character offsets for aesthetic purposes. Also, using any nonzero amount of tracking disables nonessential ligatures, whereas kerning attempts to maintain ligatures.
⬇ Note
If you apply both the Tracking and Kerning modifiers to a layer, the layer applies the tracking and ignores the kerning.