The question mark (?; also known as an interrogation point, interrogation mark, question point, query or eroteme), is a punctuation mark that replaces the full stop (period) at the end of an interrogative sentence in English and many other languages. The question mark is not used for indirect questions. The question mark character is also often used in place of missing or unknown data.
Origin: Long ago when scholars wrote in Latin, they would place the word questio – meaning “question” at the end of a sentence to indicate a query. Soon questio was shortened to qo to save space when writing, but this caused a different problem – readers might mistake it for the ending of a word. So they squashed the letters into a symbol (a lowercased q on top of an o). Over time the o became just a dot and the q changed into a squiggle, giving us our current question mark.
* Try not to use question marks with other marks. It is considered bad to use a question mark in combination with other marks. In Japan, you may see this type of usage in manga books. Especially when translated from Japanese into English → !?
Question marks can be used with other marks in informal prose to convey complex tones though: He told you what!? This combination (or similar combination) of punctuation marks is sometimes called an interrobang. The interrobang currently has no role in academic prose though.