To knock on wood or to touch wood: Origin and Meaning.

What does it mean to knock on wood or to touch wood, and all about origin and meaning?
Firstly the meaning.
The way I look at it the phrase has two meanings. Firstly one would “touch wood” if you are having a streak of good luck and you do not want to tempt fate by bragging. An example would be if the sports team of your choice had won 10 games in a row and you could brag by saying that the next game would be a winner as well, “ …touch wood”. This would be a kind of help against tempting fate.
The second meaning could be to help against bad things happening. An example would be ….” I am going to Europe for the holidays, touch wood”. Implying that you want to go on leave unless something unforeseen, usually negative, occurs to put an end to your plans.
The origin part is not so clear, and there are three possibilities most often cited.
Version 1
This version relates to the cross on which Jesus was crucified. Some maintain that splinters of the cross were sold as tokens of good luck. To have a piece of the cross on your person was considered good luck. No much to substantiate this origin.
Version 2
In Pagan times it was believed that both good and bad spirits lived in trees. One would knock on the tree to deafen the bad spirit as to what you were saying, so the bad spirit could not hear and cause bad things to happen. There was also a good spirit, and knocking on the tree would result in good luck, a prayer.
Version 3
This one is probably the most plausible. Originated from a children’s game called “Tiggy touch wood”. You could not be tagged if you touched wood. From the early 1800’s.
There is hardly a country in the world that does not have an expression similar to this one. The list and meanings can be found at Wikipedia , search for “knocking on wood”.
Wikipedia is a good starting point for further digging