In science, tolerance is the ability of a living organism to support the chemicals or physical effects of other elements without damage. We talk about intolerance when this organism can’t support the element.
The moral meaning of tolerance is the act of approving something that we wouldn't have usually approved. For example, we can allow someone to make noise when we would usually demand silence. One can also tolerate a margin of error for a work.
Justice needs tolerance to exist because it allows us to consider that everyone makes mistakes and we need to try to understand everyone’s situation, rights and motivations before judging (see justice).
Tolerance also refers to the state of mind of someone opening to others by admitting that there’s other ways of thinking and acting than their own.
Tolerance is a virtue that makes us respect what we wouldn’t usually accept, for example something that would go against our convictions and beliefs. For example, religious parents who are tolerant with their homosexual child.
However, being tolerant does not mean really accepting someone else’s difference. It only means that you won’t reject or attack them because they are different, you will just control yourself to remain kind. But we may say that tolerance is the first step to true acceptance.