Knock on Wood; Touch Wood

What does the idiom “Knock on Wood; Touch Wood” mean?


Let’s hope I have good luck or continue to have good luck.

For example:

“By tomorrow night, knock on wood, I’ll be in Sydney.”


This is possibly of Druid origin, referring to the propitiation of tree spirits. “Touch wood” is more common in the UK, but is used in the USA as well.