An iSCSI target is a logical target-side device that hosts iSCSI LUNs and masks to specific iSCSI initiators. You need to configure the iSCSI initiator to discover the iSCSI target so that the ESXi host can access LUNs on the target.
ESXi hosts support the two methods of iSCSI target-discovery:
1. static discovery – the IP address (or the host name) and the iSCSI name of the target are manually specified. The iSCSI initiator doesn’t have to perform the discovery.
2. dynamic discovery – all iSCSI targets associated with an IP address (or a host name) and the iSCSI name are discovered. An ESXi host issues the iSCSI-standard SendTargets command to the target. This target then responds with all the available targets and LUNs to the ESXi host.
The following picture illustrates the iSCSI target-discovery process (source: VMware):