Faith (in the sense that I think the thread starter meant) is the belief in something despite (or ocassionaly because of) the complete lack of evidence. It is the antithesis of a rational belief which is one held due to positive evidence. So, faith can be considered to be synonomous with "irrational belief".
If the something has evidence for it, then faith is not required, and hence the belief is a rationally held one.
Articles of belief which require faith are often coupled with; ideas promoting faith (i.e. the irational belief in something) as a positive thing, or general lack of evidence being a special form of positive evidence, or both (e.g. Christianity's demonizing of "Doubting Thomas", the man who asked for actual evidence, rather than taking things at face value, or the Conspiracy Theorist who points to complete lack of corroborating evidence as proof of "just how powerful" the conspirators are).
A second meaning of faith is perhaps synonomous with "trust". e.g. "I have faith in my friends". This is based on prior experience with your friends and knowing that they are of good character and so on. Hence "having faith in someone" is not (necessarily) irrational. This is a second, quite seperate, meaning of the word faith.
__________________
|