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 now use only the APL385 Unicode font for displaying source code and session logs. With most modern browsers, on PCs, Macs, IPhones and iPads, the font will display correctly whether or not the font is installed. For older browsers (2008 and earlier) and for Safari on Mac OS X you need to download and install the font.
The embedding technology is described in “Understanding font embedding”. Not all APL web sites use this technology. We generally recommend downloading and installing the APL385 Unicode font for best results on the Web.