What does key represent for a table record

Hello Experts,

Can anyone explain what this Key here stands for?

We have a page showing BO data, from the logic it was written i can see when trying to delete current record, it is referring to this key to call the REST for delete. But now it is giving error because not able to find the record based on that key value. When i looked at the log it appears that the key is not equal to Id of the data record. Just wondering what the key value stands for and How is the key value generated?

Thanks

Gabriel