From UBC Wiki

provides a reason for a belief or action that counts in favour of adopting the belief or performing that action. note that a reason might explain someone's belief or action as well as provide justification for their belief or action.

example of a justifying reason for an action: Sam does not eat pork because he is Muslim

example of a justifying reason for a belief: Linda believes that climate change is caused by humans based on the best scientific evidence for this (e.g. rate of climate change acceleration as calculated by using ice cores, fossil records, tree rings etc.)

Careful, on many theories of justification, a belief can be justified but nevertheless false. That is, we can have good, rationally compelling reasons for holding the belief but it turns out that the belief is not true.

example of a belief that is justified but false: suppose that you know that Sam is Muslim, ceteris paribus you would be justified in believing that Sam does not eat pork. However, it could still turn out that he does eat pork. If that is the case, then your belief is justified but false.