What is a hash in cyber security?

Can you explain to me what exactly a hash is in the context of cybersecurity? I understand it's some kind of code or function, but I'm not quite clear on how it works and why it's important. Can you give me a simple, easy-to-understand definition and some examples of how hashes are used in the field of cybersecurity? Additionally, are there any specific types of hashes that are commonly used, and how do they differ from one another? Thank you in advance for your help.