This is a Gauge32 index number identifying which instance/fragment one stored fragment of a certificate/key used to secure the connection to the external VMM represents within its parent key or certificate object. Certificate or key material for that key fragment can be split across multiple stored instances, and this index is what lets UCS Manager reassemble them in the correct order rather than concatenating them arbitrarily. An inst value of 0 followed by inst 1 for the same parent tells an admin those two records together make up one complete key, in that order.