Faith has a few definitions. In fact, it has a lot of definitions, to the point that the word entering any conversation often obfuscates and confuses the discussion.
- Belief in a god.
- Accepting a claim as true without sufficient evidence
Keep in mind that atheists don't have a problem with all the definitions. Instead we'll address the pertinent definition.
Faith is an strong form of belief (accepting a claim as true), where what you're accepting is either:
- Unsupported by valid evidence
- Is contradicted by valid evidence
If one's belief is backed up by good valid evidence, it is not faith. For instance, it does not take faith to think one can fly in an airline and survive. Plenty of evidence exists that demonstrates the relative safety (over say, driving in a car) of air travel.
The objection that atheists have with faith is not that it is a belief. It is that one is accepting something as true without it being supported by good evidence.
That seems foolish to critical thinkers. The time to accept a claim as true is when it is been sufficiently demonstrated.