How valid is this statement? "A belief is what we accept as truth."

Many people have many beliefs and according to how they perceive the world that's what the truth is. If a truth is an objective term regardless of the people who observe it, that does not mean that people will perceive it as such and there is high chance that what is truth will fall within someone's belief system, while often even things that are not truth or are considered to be wrong are also parts of the belief system of a person. When a person's belief coincides with something that is considered to be a general truth and the person understands why it is so then it is considered by many to be knowledge. In addition, if a person spends their entire life without finding out what the truth actually is, the person will always consider their belief to be truthful so it doens't even matter for them whether they're wrong or not wrong since it won't matter. Ultimately, everything is highly subjective and the statement can be extremely valid or not valid at all, depending how open-minded the person you're talking to is.

I think that statement is really valid, especially in the context of social, philosophical, or religions.

Without we even realize, we often unconsciously perceive existing information according on how we want to see it (depending on what make us satisfied the most), not how it actually happens.

This often creates a certain bias on what we believe in because people have different things that influence their satisfaction.

So in the end, a belief is something that we personally accept as truth.