about; regarding; related to
に関する is a formal noun-modifying phrase meaning 'about' or 'regarding', used to connect a topic to a following noun.
に関する is the dictionary form of the verb 関する ('to be related') combined with the particle に. It acts like a single modifier that describes a noun. It is equivalent to 'about' or 'concerning' in English, but it always comes before a noun, not at the end of a sentence. For example, you can say 環境に関する問題 (environment-related problems), but you cannot say *環境に関するです. Instead, you use について for a topic in a sentence, like 環境について話す (talk about the environment).