What is a Gap?

What is a gap?
Is it formed by price movemements while a broker is ‘closed’?
With forex only being ‘closed’ over weekends, it should only be possible to have gaps after a weekend?

Yes & yes.

Go back and look at what most of the pound pairs did on sunday. Now thats a gap. Also you should know that many traders will buy or sell in the opposite direction of the Gap with the hope that it will close, and it usually does.

I guess it depends on your broker
Oanda was open while the GBP was falling so there was no ‘gap’ on my charts
I have never actually seen a gap on Oanda as they never really close…

What interests me is why people would trade the gap different to any other price movements?