I had to define faith for myself and once I did, I left all religions behind. I made up this saying, which I thought was original at the time, but who knows.
"Faith is the absolute belief in something that may or may not exist"
Once I started saying that, I could no longer accept anything on faith. It also goes along with "Perception is Reality".
I also think faith and naivity go hand in hand. You have to have a certain level of naivity to have faith. Faith is also the putty religions use to fill in the gaps of the things which can't possibly be explained. I think for many there is a certain spiritual calm to having faith, but for me it was only a way to lie to myself.