...is believing in the existence of something that we cannot prove exists.
Many people don't realize what an incredible leap of faith we take every day by trusting that the world around us is actually the world around us. Prove to me that you all exist, and that I am not just a disembodied brain in a vat, being fed stimuli and responses that simulate a real world...
Faith is different than Faith in God. We all have Faith at some level. What we have Faith in is where the arguments start.