The term Hash Algorithm (abbreviated SHA for safe hash algorithm) refers to a group of standardized cryptographic functions. These are used to calculate a check value for any digital data (messages) and are among other things the basis for creating a digital signature.

The check value is used to ensure the integrity of a message. If two messages produce the same check value, the equality of the messages should be guaranteed in their normal discretion, without any intentional manipulation of the messages. For this reason, a cryptographic hash function calls for the property of collision security: it should be practically impossible to generate two different messages with the same check value.

Source: https://de.wikipedia.org/wiki/Secure_Hash_Algorithm