Relevant means having some reasonable connection with something. When used in the context of a evidence law, it refers to the evidence's tendency to prove or disprove a matter of fact that is related to an issue in dispute in the case. A common basis for an objection to testimony or physical evidence is that it is "irrelevant."
Not all relevant evidence is necessarily admitted in a lawsuit. Relevant evidence may be excluded in the judge's discretion for certain reasons, such as having a prejudicial effect on the minds of the jury.