Harvard

'Secondary referencing' is the term for when you want to reference a source that is quoted in something else.  Good academic practice is to go back to the original text, read the quote in context and then cite that directly but sometimes this isn’t possible. 

So, for example, the article that you are reading by Skelton (2011) cites Festinger’s (1957) book, and you want to use Festinger’s excellent idea in your essay.  In this case you might decide to use Festinger’s words that Skelton quotes and, to do this, you will use a form of secondary referencing. 

Festinger’s (1957, cited in Skelton, 2011, p.258) ideas that dissonance is inevitable …

Feelings of dissonance are inevitable if implicit values are denied in practice (Festinger, 1957, cited in Skelton, 2011, p.258) ...

You will always include the source that you did read, in this example Skelton, in your References list.  Do not list Festinger in your References, because you did not read this source.