Quotation marks in English
In English writing, quotation marks or inverted commas, also known informally as quotes, talking marks, speech marks, quote marks, quotemarks or speechmarks, are punctuation marks placed on either side of a word or phrase in order to identify it as a quotation, direct speech or a literal title or name. Quotation marks may be used to indicate that the meaning of the word or phrase they surround should be taken to be different from (or, at least, a modification of) that typically associated with it, and are often used in this way to express irony. (For example, in the sentence 'The lunch lady plopped a glob of "food" onto my tray.' the quotation marks around the word food show it is being called that ironically.) They are also sometimes used to emphasise a word or phrase, although this is usually considered incorrect. 
Double typographic quotes
Quotation marks are written as a pair of opening and closing marks in either of two styles: single (‘...’) or double (“...”). Opening and closing quotation marks may be identical in form (called neutral, vertical, straight, typewriter, or "dumb" quotation marks), or may be distinctly left-handed and right-handed (typographic or, colloquially, curly quotation marks); see quotation mark glyphs for details. Typographic quotation marks are usually used in manuscript and typeset text. Because typewriter and computer keyboards lack keys to directly enter typographic quotation marks, much of typed writing has neutral quotation marks. Some computer software has the feature often called "smart quotes" which can, sometimes imperfectly, convert neutral quotation marks to typographic ones.
The typographic closing double quotation mark and the neutral double quotation mark are similar to – and sometimes stand in for – the ditto mark and the double prime symbol. Likewise, the typographic opening single quotation mark is sometimes used to represent the ʻokina while either the typographic closing single quotation mark or the neutral single quotation mark may represent the prime symbol. Characters with different meanings are typically given different visual appearance in typefaces that recognize these distinctions, and they each have different Unicode code points. Despite being semantically different, the typographic closing single quotation mark and the typographic apostrophe have the same visual appearance and code point (U+2019), as do the neutral single quote and typewriter apostrophe (U+0027). (Despite the different code points, the curved and straight versions are sometimes considered multiple glyphs of the same character.)