Touch Wood Meaning

Example: To make contact with wood to avert bad luck, in accordance with a folk practice.
1930, John D. Stephenson, The Structure of English from Sentence to Essay, page 105,
  Touching wood possibly has reference to (a) the cross, or (b) the altar rails in days when criminals could take sanctuary in churches.
2003, Chester Schneider, The Making of a Christian Psychiatrist, Xulon Press, US, page 193,
  Very few patients for whom I provided psychiatric treatment ended their lives by suicide, but I became increasingly convinced that my residency instructor who touched wood because none of his patients had killed themselves had not been treating many seriously mentally ill patients for any extended period of time.
2010, Rhena Branch, Rob Willson, Cognitive Behavioural Therapy For Dummies, John Wiley & Sons, UK, 2nd Edition, page 102,
  Examples of rituals include touching wood, repeating phrases in your mind, wearing lucky clothes or jewellery, and avoiding unlucky numbers, out of a faulty belief that these rituals will stop unfortunate or tragic events befalling yourself or your loved ones.