Also to reduce invalid characters in URLs to valid characters: spaces are converted to + signs, and all other invalid characters are converted to their ASCII number in hexadecimal, preceded with a %.

Example: "Tom's Cabin" becomes "Tom%27s+Cabin"

Button on keyboards, usually top left.
The act of putting the printed character associated with the escape key (ASCII code 27 / 1B hex) into a file: was used a lot with ANSI coloured text. A real bastard to put into your text tho, as pressing Esc, dialing in on the numeric keypad (Alt+27) or most other ways ended up quitting the program.