Character styles apply to the contents of one or more runs of text. They have a type attribute value of character. They are referenced by the <w:rStyle> element within a run's properties element (<w:rPr>).
The above character style is then applied in content as shown below.
Child Elements of Character Styles (<w:style w:type="character">):
There is only one element.
For the details of the run or text properties that are specified within rPr, see Text - Formatting.
Reference: ECMA-376, 3rd Edition (June, 2011), Fundamentals and Markup Language Reference § 184.108.40.206.
Below is a style definition for text that might appear in an external stylesheet.
The style is then applied as shown below.