What is a new persistent cough?

[lordofthefence]

Can someone please explain to me how often you need to be coughing for it to be considered a persistent cough?

I keep hearing people say the advise is clear, but no one has clarified this.

As far as I can tell its a cough that would lead you to think 'I have a cough' so not a one off, or down to something going down the wrong way.