OID is an acronym for object identifier. It is an extensively used identification mechanism developed jointly by the International Telecommunication Union and the International Organization for Standardization used for naming any type of object, concept or "thing" with a globaly unambiguous name.
What this means in the world of electronic health records is that obtaining an OID code ensures that the identifiers you use in your organization are distinct from those used by another organization. So asking you to obtain an organizational OID code from the HL7/OID registry and inputting it into the software grants authority access to allow My Vision Express to create additional OIDs for each patient, visit, and other factors which helps distinguish your information from all other information that is processed and later shared.
To view instructions on how to obtain an OID for your practice, go to the article for How to Request an OID.