An ink trap is a feature of certain typeface

Typeface

In typography, a typeface is the artistic representation or interpretation of characters; it is the way the type looks. Each type is designed and there are thousands of different typefaces in existence, with new ones being developed constantly....

s, where the corners or details are removed from the letterforms. When the type is printed, ink

Ink

Ink is a liquid or paste that contains pigments and/or dyes and is used to color a surface to produce an image, text, or design. Ink is used for drawing and/or writing with a pen, brush, or quill...

 naturally spreads into the removed area. Without ink traps, the excess ink would blob and ruin the crisp edge.

Ink traps are only needed for small point sizes and are usually only found on typefaces designed for printing on newsprint

Newsprint

Newsprint is a low-cost, non-archival paper most commonly used to print newspapers, and other publications and advertising material. It usually has an off-white cast and distinctive feel. It is designed for use in printing presses that employ a long web of paper rather than individual sheets of...

. Fonts of this kind are applicable for classifieds

Classified advertising

Classified advertising is a form of advertising which is particularly common in newspapers, online and other periodicals which may be sold or distributed free of charge...

 or telephone books

Telephone directory

A telephone directory is a listing of telephone subscribers in a geographical area or subscribers to services provided by the organization that publishes the directory...

.

Fonts featuring ink traps include Kurier and Bell Centennial

Bell Centennial

Bell Centennial is a sans-serif typeface designed by Matthew Carter in the period 1975–8. The typeface was commissioned by AT&T as a proprietary type to replace their then current directory typeface Bell Gothic on the occasion of AT&T’s one hundredth anniversary...

.