APL is famously symbolic rather than lexical: its primitive functions and operators are denoted by single, non-alphabetic symbols rather than by words. APL programmers use keyboard mappings to type APL.
In the past they also used special fonts. The spread of Unicode has made these redundant except for displaying pre-Unicode source code or output, or running older interpreters. (J, kdb and q instead draw their symbols from the ASCII character set.)
Vector and the APL Wiki use only the APL385 Unicode font for displaying source code and session logs. With practically all modern browsers, on PCs, Macs, tablets and smart phones the font will display correctly whether or not the font is installed. For older browsers (2008 and earlier) you might need to download and install the font.
The embedding technology is described in “Understanding font embedding”.