Here’s a glossary of common type terminology, which along with the FAQs may answer many font related questions. If the information you need isn’t here, call us.
Oldstyle figures (OSF)
- Numbers that have different heights, some aligning to the baseline, some below. Oldstyle figures harmonize well with lowercase letters. Using oldstyle figures helps keep the numbers from standing out too much and disturbing the overall flow of the typography on the page.
When the different figure sets are built-in as OpenType features, certain (older) operating systems and applications will only be able to access the default figures
See Figuring It Out: OSF, LF, and TF Explained on The Fontfeed.