Introduction
A font is a character style one may choose from in programs that support using them. Many fonts are available for Ubuntu users to choose from.
Font packages available in the Ubuntu repositories
fonts-crosextra-caladea - Sans-serif font metric-compatible with Cambria font
fonts-crosextra-carlito - Sans-serif font metric-compatible with Calibri font
lmodern - scalable PostScript and OpenType fonts based on Computer Modern
ttf-goudybookletter - Old style roman font
ttf-levien-museum - metal Centaur fonts revival family
ttf-mplus - M+ sans serif fonts with different weights
ttf-mscorefonts-installer - Microsoft TrueType core fonts
ttf-ubuntu-font-family - Ubuntu Font Family, sans-serif typeface hinted for clarity
ttf-khmeros - KhmerOS Unicode fonts for the Khmer language of Cambodia
fonts-liberation - Fonts with the same metrics as Times, Arial and Courier
ttf-sil-padauk - smart Unicode font for languages in Myanmar
fonts-thai-tlwg - Thai fonts for Garuda, Kinnari, Loma, TlwgMono, Norasi, Purisa, Sawasdee, TlwgTypewriter, TlwgTypist, TlwgTypo, Umpush, and Waree.
ttf-tmuni - font for Tibetan, Dzongkha and Ladakhi (OpenType Unicode)
gsfonts - Fonts for the Ghostscript interpreter(s)
ttf-dejavu and ttf-dejavu-extra - Vera font family derivate with additional characters
otf-freefont - otf-freefont: Freefont Serif, Sans and Mono OpenType fonts
ttf-freefont - ttf-freefont: Freefont Serif, Sans and Mono Truetype fonts
ttf-indic-fonts - Metapackage for free Indian language fonts: Bengali, Devanagari script, Gujarati, Kannada, Malayalam, Oriya, Punjabi, Tamil, and Telugu
ttf-bitstream-vera - The Bitstream Vera family of free TrueType fonts
ttf-adf-accanthis, ttf-adf-baskervald, ttf-adf-berenis, ttf-adf-gillius, ttf-adf-ikarius, ttf-adf-irianis, ttf-adf-libris, ttf-adf-mekanus, ttf-adf-oldania, ttf-adf-romande, ttf-adf-switzera, ttf-adf-tribun, ttf-adf-universalis, and ttf-adf-verana - Fonts of the Arkandis Digital Foundry: Accanthis, Baskervald, Berenis, Gillius, Ikarius, Irianis, Libris, Mekanus, Oldania, Romande, Switzera, Tribun, Universalis, and Verana
ttf-ancient-fonts - Unicode Fonts for Ancient Scripts
ttf-anonymous-pro - fixed width sans serif font designed for coders
ttf-droid - handheld device font with extensive style and language support
ttf-aenigma - 465 free TrueType fonts by Brian Kent
ttf-sil-gentium-basic - smart Unicode font families (Basic and Book Basic) based on Gentium
t1-xfree86-nonfree, ttf-xfree86-nonfree, and ttf-xfree86-nonfree-syriac - non-free fonts from XFree86: Postscript Type 1, TrueType, and syriac OpenType.
ttf-bpg-georgian-fonts - BPG Georgian fonts
ttf-marvosym - Symbol font for school and office
ttf-farsiweb - free TrueType fonts for Persian language
ttf-sinhala-lkmug - Unicode Sinhala font by Lanka Linux User Group
ttf-fifthhorseman-dkg-handwriting - font that imitates Daniel Kahn Gillmor's handwriting
ttf-inconsolata - monospace font for pretty code listings and for the terminal
ttf-gfs-didot-classic - greek font family (Classic Didot revival)
ttf-gfs-bodoni-classic - smart greek typeface revival
ttf-gfs-neohellenic - new Greek font family with matching Latin
ttf-century-catalogue - century-style font revival
ttf-konatu - TrueType Font originally for BeOS
texlive-fonts-recommended - TeX Live: Recommended fonts.
Arabic Fonts
ttf-sil-scheherazade - smart Unicode font for Arabic
ttf-arabeyes - Arabeyes GPL TrueType Arabic fonts
Chinese, Japanese, and Korean Fonts
ttf-wqy-microhei - A droid derived Sans-Seri style CJK font
ttf-wqy-zenhei - "WenQuanYi Zen Hei" A Hei-Ti Style (sans-serif) Chinese font
ttf-dejima-mincho - antique-looking Japanese TrueType Mincho font
ttf-umefon - Japanese TrueType font, Ume-font
ttf-takao, ttf-takao-gothic, ttf-takao-mincho, and ttf-takao-pgothic - Japanese TrueType font set: Takao Fonts, Takao Gothic Fonts, Takao Mincho Fonts, and Takao P Gothic Fonts.
ttf-kochi-gothic and ttf-kochi-mincho - Kochi Subst Gothic and Mincho Japanese TrueType font without naga10
ttf-sazanami-gothic and ttf-sazanami-mincho - Sazanami Gothic and Mincho Japanese TrueType font (legacy)
ttf-nanum-coding - Nanum Coding fixed width Korean TrueType font
fonts-nanum and fonts-nanum-extra - Nanum and additional Nanum Korean fonts
ttf-baekmuk - Baekmuk series Korean fonts
Manually installing a font in Ubuntu
If you have a font file (.ttf) that is not available from the Ubuntu repositories, and you would like to use it in Ubuntu, one will want to manually install the font. For example, if one had SLIDA.ttf as the font file, one would perform the following via a terminal:
sudo mv SLIDA.ttf /usr/share/fonts sudo fc-cache -f -v
Known Issues
[needs-packaging] ttf-kouzan-mouhitu - https://bugs.launchpad.net/ubuntu/+bug/567553
[needs-packaging] ttf-indonesian - https://bugs.launchpad.net/ubuntu/+bug/688780
[needs-packaging] Google Fonts - https://bugs.launchpad.net/ubuntu/+bug/648873
External Links
http://pkg-fonts.alioth.debian.org/ Debian Fonts Task Force with a list of all fonts available for Debian. https://wiki.debian.org/SubstitutingCalibriAndCambriaFonts Debian article on dealing with Calibri and Cambria fonts