The exclamation - ! - is a punctuation mark used in English and other languages to denote an exclamatory statement such as extreme happiness, shouting, or surprise. Also used in some math and computer programming languages. The mark used as an exclamation was originally a way of writing IO, a Latin word meaning exclamation or expression of joy.
Two theories as to the form of the exclamation are:
1) Scribes saved space by putting the I above the O with the O eventually becoming a filled-in dot;
2) It was originally written as an O with a slash through it but the O eventually disappeared (or became the dot) and the remaining slash evolved into today's exclamation mark.
Usage of the Exclamation Point
Exclamatory Sentence That is a ridiculous thing to say!
Exclamatory Question Did you really say that! (Or, you could use an interrobang instead.)
Multiple Exclamation Points Wow!!!!! (not good grammar & punctuation)
Notes on Exclamation Points from About.com Grammar & Composition
"Since it first popped up in the 14th century, the exclamation point (punctus admirativus or exclamativus) has generally been regarded as the hot-headed punk in the school of punctuation.... As a result, most professional writers view exclamations as a bad habit to break or an awkward stage to outgrow."
Also Known As: exclamation point | exclamation mark | exclamation note
Slang Terms: bang; pling; smash; soldier, control; screamer
Examples: Wow! Unbelievable! That's great! Stop jumping on the bed this instant!
Use exclamation marks sparingly in text. Multiple marks such as "Good Grief!!!!!!" are not standard usage.
Although exclamations can take many forms, the examples here (sidebar) show typical styles: Rounded/tear drop with circle; Rectangle/Tapered over diamond; Rectangle/Tapered over square; Rectangle/Tapered over circle.