What is the hash of a malware?

Could you please elaborate on what exactly is meant by the "hash of a malware"? Specifically, how is this hash generated, and what role does it play in identifying or analyzing the malware? Furthermore, are there any common hashing algorithms used specifically for malware analysis, and how can this hash be utilized to detect or prevent future infections? Lastly, are there any specific challenges or considerations that practitioners should be aware of when dealing with malware hashes?