What is the difference between TT, KBD, SAMP?

TT: - This tag displays text in monospace “teletype” font. This is useful to create “teletype” text. SAMP: -This tag styles text as sample program output. The ouput is usually displayed in a monospace font. KBD: -This displays the text the user is supposed to enter, usually in bold or standard monospace font. The text which the user should enter is displayed in monospace font.