TTF is the font container format developed by Apple in the late 1980s and adopted by Microsoft in Windows 3.1. Stores quadratic Bézier glyph outlines, hinting data, and font metadata (kerning, OS/2 flags, naming). Every operating system reads TTF natively. Mostly superseded for web use by WOFF/WOFF2 (smaller compressed wrappers around the same SFNT data) but TTF remains the source format and the universal install target.
How to open
Double-click on any OS to preview + install. Font management tools (FontBook on macOS, Windows Fonts, Linux fc-cache) handle batch installs. To use on the web, convert to WOFF2 first.