In a secular context, "faith" refers to the act of adhering to a particular belief in spite of
- the absence of substantial supporting evidence
- the existence of overwhelmingly contradictory evidence
In general, then, it means belief without regard to evidence, though there are different levels of this.
By convention, the belief in question must be one that has a beneficial outcome, especially if the benefit isn't just to one's self but rather to the audience to whom one is speaking. An athlete might speak of having "faith" that the team would win the game or that s/he would play especially well (benefiting the team and its fans), but not that s/he would be the one to make the winning shot (benefiting only her/himself).
The word "faith" by itself is commonly used to refer to faith that is specifically of a religious nature, as in "people of faith".
In the best sense of the word, it can mean "trusting one's instincts in spite of seemingly-logical arguments to the contrary". This may be a rational thing to do when one has a strong sense that the "seemingly-logical arguments" are in fact flawed or distorted in some way (i.e. involve some kind of rhetorical deception, whether intentional or otherwise) but does not have the resources to work out the flaw and frame a counter-argument prior to making a decision.
The idea of "faith" is commonly seen or presented as a positive force, given the positive usage above in which an intuitive "short-cut" to a rational decision allows a better outcome within a limited time-frame than does any available fully-documented rational process. This usage, however, becomes conflated with the religious sense of the word, implying that religious beliefs are somehow nobler or more beneficial than rational ones.