Lucida /ˈluːsɪdə/ is an extended family of related typefaces designed by Charles Bigelow and Kris Holmes in 1985. The family is intended to be extremely legible when printed at small size or displayed on a low-resolution display - hence the name, from 'lucid' (clear or easy to understand).
There are many variants of Lucida, including serif (Fax, Bright), sans-serif (Sans, Sans Unicode, Grande, Sans Typewriter) and scripts (Blackletter, Calligraphy, Handwriting). Many are released with other software, most notably Microsoft Office.
Bigelow & Holmes, together with the (now defunct) TeX vendor Y&Y, extended the Lucida family with a full set of TeX mathematical symbols, making it one of the few typefaces that provide full-featured text and mathematical typesetting within TeX. Lucida is still licensed commercially through the TUG store as well through their own web store. The fonts are occasionally updated.
The Lucida fonts have a large x-height (tall lower-case letters), open apertures and quite widely spaced letters, classic features of fonts designed for legibility in body text. Capital letters were designed to be somewhat narrow and short in order to make all-caps acronyms blend in. Bigelow has said in interview that the characters were designed based on hand-drawn bitmaps to see what parts of letters needed to be clear in bitmap, before creating outlines that would render as clear bitmaps. The fonts include ligatures, but these are not needed for text, allowing use on simplistic typesetting systems. X-heights are consistent between the fonts. Hinting was used to allow onscreen display.