what is a quintile?

Today a family member asked me about a word in The Age newspaper - quintile. I asked her to read the sentence containing the word and she read:

The preliminary results showed the richest quintile of households received about 12 per cent of social assistance benefits while the second richest quintile got 11 per cent. 

I sounded like the word quartile, which I knew had something to do with quarters. [Here's the definition from Math Dictionary.] So I suggested quintile might relate to fifths.

And it does. The opening line of the article in The Age said:

The richest fifth of households receive nearly half of all the wages paid in Australia - but also get about 12 per cent of all government handouts, new research by the Bureau of Statistics show. 

Here's a more exact definition of the word from the Merriam-Webster