Understanding Figure Styles
Figures, also referred to as numerals or numbers, are a frequently-appearing element in typesetting. Ilene Strizver explains meaning of lining and oldstyle, tabular and proportional figures.
Read the article at creativeLIVE blog http://blog.creativelive.com/understanding-figures-styles.
When choosing a font(s) for a project, consider what kind of numerals appear in the text, and then select a font that offers the style(s) of figures you need.