You may see single or double quotation marks used to mark out idiomatic or unfamiliar expressions
Examples
• I've always thought that he was very annoying, a bit of a 'pain in the neck.'
• I'm not sure what you mean by "custodial care", but I'm sure you will explain it to me.
Quotation marks both single and double are also used for specific purposes in bibliographic references or when citing sources in academic writing. There are a number of ways of organising bibliographies which set out standard formats. Most organisations and academic institutions will prefer one of these or have their own format published in a 'style guide'.