What does Blood oath mean?

Blood oath meaning in Urban Dictionary

Traditionally a blood oath had been when one could lose their blood(Cut yourself or something) and supply it onto a altar or whatever they thought right(sometimes a religious action) and swore to uphold a particular task, it doesn't matter what. Plus it ended up being when a person(s) would shed bloodstream, generally they would cut their particular hand and then shake hands in contract to an activity they swear to support.More modernly it simply means you swear to complete something it doesn't matter what, and because it really is a blood oath, modernly this means hurting as well as killing others in oath, therefore 'blood' oath, indicating blood would be shed in promise to the task, generally a phrase just employed by mobsters and crooks.