What is a 'big ask'?

A 'big ask' is an informal idiom describing goal/task that is difficult to complete. It has migrated from British/Australian the discussion of sport into more general English. 


The always enjoyable Dot Wordsworth points out that the use of 'ask' as a noun goes back a thousand years. She also reminds us to take care with pronunciation lest 'ask' be misheard.