When IRTC loaded you will have noticed the word Host, before the date, on the top right of the screen. This mode is used when you wish to use the PC and its resources without any communication with the Remote Target. You may wish to perform some inspection of the Target image memory for example. All references to Forth kernel words, like @, !, + etc., will be from the Host definitions. That is those definitions that relate to the 80X86 processor in the PC.
After you type ?REM, Ctrl+R, you will now see Remote instead of Host. This indicates that where applicable IRTC will use the Remote Target for execution of the Target word definitions. This means that you now have two Forth's running together. The Host controls everything through IRTC but execution occurs in the Remote Target. When you type on the PC keyboard the Host parses your input and performs the necessary actions to instruct the Remote Target what to do. The Target is a slave, but does execute the run-time code in real time.
The console window title bar indicates the mode. The Vocabularies that will be searched are modified by the mode selection. When in the Host mode the first two will be METAAVR. This is the IRTC vocabulary. When in the Remote mode the first two will be METAAVR and TARGET. The TARGET vocabulary holds all the AVR Forth definitions for the Remote Target. This will be the first vocabulary searched, so @, !, + etc. will now be the Remote versions and not the 80X86 versions of the Host if they are compiled.