A five couple longsways set.
Longways means that you are in couples, facing your partner in a long line stretching away from the band. Or rather, not one long line but two lines with all the men on one side facing all the women on the other. If you look 'up' the set to see if the band's still there, the man have the ladies on their right (or read that also as the ladies have the men on their left)
When back at the top of the set the first couple face each other and all the other people face up.
All the men are on one side and all the women on the other and the pattern is a sort-of up-side-down horseshoe.
If you are second, third, fourth (etc) couple dancing up the set, you will be doing the same, right hand, left hand, right hand etc. You are dancing along the line of that up-side-down horseshoe (or according to Mr Pott's description, up one trouser leg and down the other)