Typography can be loosly defined as the styling of text. In interpreting meaning from writing, typography can play a critical role in "setting the tone" so to speak.

"Typography is the visual component of the written word" — Matthew Butterick


The arrangement of type typically invovles the following:
• typefaces - the variation in size, weight, slope, width, etc. of text
• point sizes - the scale of the text
• line length
• line spacing - the height of each individual line (also called leading)
• letter spacing - the space between each letter
• bi-letter spacing - the spacing between pairs of letters (also called kerning)

Further Reading

- Detail in typography
- Better Web Typography
- pimpmytype.com