The full form of PRNT SCRN is Print Screen

Print Screen (often abbreviated Print Scrn, Prnt Scrn, Prt Scrn, Prt Scn, Prt Scr, Prt Sc, Pr Sc or PS) is a key present on most PC keyboards. It is typically situated in the same section as the break key and scroll lock key. The print screen may share the same key as system request.

Under command-line based operating systems such as MS-DOS, this key causes the contents of the current text mode screen memory buffer to be copied to the standard printer port, usually LPT1. In essence, whatever is currently on the screen when the key is pressed will be printed. Pressing the Ctrl key in combination with Prt Sc turns on and off the “printer echo” feature. When echo is in effect, any conventional text output to the screen will be copied (“echoed”) to the printer. There is also a Unicode character for print screen, U+2399 ⎙ PRINT SCREEN SYMBOL.