What did Abe Simpson from The Simpsons mean whn he said this?

In the episode where Homer and Marge try to spark up their marriage
again and all, you kmow the one, where they are in the mini golf
course and steal the hot air balloon and all.
Well, when Abe (Granpa) was babysittin the Kids, he said "Lisa, run
outide and go cut me a switch", WTF does this mean ?? lol
what does it mean tho? explain