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What is a Font?

A font is a collection of glyphs — visual representations of characters — designed with a unified visual style and packaged into a file that software can use to render text. In everyday speech "font" and "typeface" are used interchangeably, but there is a technical distinction: a typeface is the design family (e.g., Helvetica), while a font originally referred to a specific weight and size within that family (e.g., Helvetica Bold 12pt). In digital usage, a font file contains an entire typeface family or a single style within it.

Fonts are critical to Unicode rendering. No single font covers all 154,998 characters in Unicode 16.0. Instead, operating systems use font fallback chains: when a character is missing from the primary font, the renderer automatically substitutes a glyph from the next font in the chain that contains it.

Font File Formats

Modern fonts use the OpenType (.otf) or TrueType (.ttf) formats, which are functionally equivalent containers. Web fonts are distributed as WOFF (Web Open Font Format) or WOFF2 (compressed), which are wrappers around the same data.

Unicode Coverage

Every font has a Unicode coverage — the set of code points for which it provides glyphs. Tools like fc-query (Linux), Font Book (macOS), or online tools like Wakamai Fondue reveal exactly which characters a font covers.

Fonts designed for broad Unicode support include: - Noto (Google): aims for complete Unicode coverage across all scripts - GNU Unifont: bitmap font covering the entire Basic Multilingual Plane - DejaVu Sans: covers Latin, Greek, Cyrillic, and many symbols

Variable Fonts

OpenType 1.8 introduced variable fonts, which encode an entire design space (weight, width, slant, optical size) as a single file with interpolation axes. Instead of separate Bold, Light, and Condensed files, one variable font file can render any point along those axes. This reduces HTTP requests for web fonts and enables smooth typographic animations.

/* Variable font usage in CSS */
@font-face {
  font-family: "Inter";
  src: url("Inter.var.woff2") format("woff2-variations");
  font-weight: 100 900;
}

h1 {
  font-family: "Inter";
  font-weight: 650; /* any value between 100–900 */
}

Quick Facts