A host may be a logical representation of a Microsoft Windows process that executes BizTalk Server artifacts like to send ports and orchestrations. A host instance is the physical representation of a host on a selected server.
A host is often either an in-process host, which suggests it's owned and managed by BizTalk Server or an isolated host, which suggests that the BizTalk Server code is running during a process that's not controlled by BizTalk course Server.
A good example of an isolated host is Internet Information Services (IIS), which hosts the receive functionality of the HTTP and SOAP adapters. Hosts are defined for a whole BizTalk Server group; a set of BizTalk Servers that share configuration, MessageBoxes, ports, and so on.
Difference between an Isolated host and an In-Process host:
The difference between an Isolated host and an In-Process is that an Isolated host must run under another process, in most cases IIS, and an In-Process host may be a complete BizTalk service alone.
Additionally, since In-Process hosts exist outside of the BizTalk environment, the BizTalk Administration Tools aren't ready to determine the status of those hosts (stopped, started or starting).
Security is additionally fundamentally different in an Isolated host versus an In-Process host. In-Process hosts must run under an account that's within the In-Process host’s Windows group, and don't maintain security context within the Messagebox.
Isolated hosts are useful when a service already exists which will be receiving messages either by some proprietary means or by another transport protocol like HTTP. In this case, the Isolated host only runs one instance of the top Point Manager and is liable for receiving messages from its transport protocol and sending them to the Messagebox through the EPM.