Faith is a tricky word with more than one meaning. (Click here for the definition of faith on Merriam-Webster.com) If you are not really careful, you can get caught in an argument that goes something like this:
1.Everyone has faith in other people.
2.Even atheists have faith.
3.Therefore it is reasonable to have faith in the teachings of Christianity.
What they don't tell you is that the definitions of "faith" in the premises is different than that in the conclusion. Take a look at that definition of faith from M-W.com. Premises 1 and 2 are associated with definitions 1 and 3, that is, trust and the strong conviction that something is true. On the other hand, the definition of faith that applies to the conclusion, 3, is definition 2. This includes "firm belief in something for which there is no proof."
I notice that there is some overlap in definition, since both trust and belief appears in definition 2. However, when one is talking about religious faith it always has some element of "firm belief in something for which there is no proof." This element is not necessarily found in the case of one person trusting another, or in expressions such as "good faith," which is defined as "honesty or lawfulness of purpose." Or in the faith in the discoveries of science, which depend on proof.
Language is tricky sometimes.
Here are links to some other articles on the subject of faith:
The Skeptic's Dictionary article on faith
Tektonics.org Article. Interesting take on faith from a Christian apologist