ORCID stands for Open Researcher Contributor ID. It is in use primarily in academic, scholarly, and STEM research.
ORCID is a 16-digit identifier, just as ISNI is. In fact, ISNI "carves out" numbers from its own database for ORCID's use so there are no data integrity issues between the two standards.
It's commonly thought that ORCID and ISNI are competing identifiers. Those who have worked on both standards would tell you that isn't true. ORCID began as a self-claiming system for individual researchers. The researcher controls the profile and what goes in it. Because ORCIDs are intended to follow a researcher's career, often the only criteria a beginning researcher has is an email address. That is the only qualification for getting an ORCID assigned to you. ISNIs have much more stringent requirements.
ORCIDs are not assigned to deceased people (so Isaac Newton, for example, doesn't have one - but he does have an ISNI!). They're primarily used in grant and funding applications. The ORCID website does allow you to link your ORCID profile to your ISNI profile.