Styles define how Mathematica notebooks, cells and expressions are formatted, displayed, evaluated and interacted with.
Styles are option sets for notebooks, cells and expressions in Mathematica defining the way expressions are displayed, evaluated and interacted with. Styles are mostly stored in stylesheets. Questions on how to define, apply and modify built-in or custom styles should use this tag.
For more general aspects of formatting text, expressions, equations, or any 2D typesetting use the tag formatting. Questions on how to format graphics might use tags graphics, graphics3d or plotting.
Useful information on stylesheets: