ESC/P is a set of printer-control commands introduced by Epson for use in printers, primarily the dot-matrix variety. Most commands are "escape sequences" consisting of the ESC character followed by various other characters, but some of the other ASCII C0 controls are also used. In some cases, numeric parameters are passed to commands in the form of binary representations, where if they are 16-bit integers, little-endian form is used.
Commands can do things such as set different character sets, fonts, and formatting, as well as transmitting bitmap graphics for printing, or cause the printer to print bar codes. The specific supported features vary between printer models.
A different command set, ESC/POS, is used in Epson point-of-sale (POS) systems.
Command languages such as this, which intersperse a few control and escape codes with mostly plain-text content sent to a printer, have mostly gone out of use in favor of fully-graphical printer drivers sending page layouts to inkjet and laser printers.