What does the expression "knock on wood" mean?

oohhh alright thank you

We call it touch wood, British English maybe? =)

That is how I call it. I’ve never actually heard of “Knock on wood before” but they probably mean the same thing.

It is for luck. If you have said something that could have jinxed you you say touch wood or knock on wood and find wood :)

They’re the same, probably exported to the US via people in wooden ships. The US version crops up in old songs and B&W musicals as well. The standard joke was to hit your head as you said it…

one of my teachers said it to scare of all the evil spirts out from the trees, cuz thats what they knocked on…trees