This chapter is about images, effects, and symbols. The only images supported are some effects that are available here.
The symbols—font-based icons—are the basis of the icon functions. The glyphs used in Bootstrap 3 are called Halflings (a reference to Lord of the Rings) and are usually not free. Bootstrap 4 no longer contains the Glyphicons, and you have to use one of the many font libraries.
Font-based icons avoid the problem of individual symbols leading to a flood of additional requests on the server. Instead, all the symbols are loaded as a font—that is, in one file. ...