Hello,
I'm sorry about the verbage, I do try to stay away from words local to the virtualisation world, but sometimes it is still the best way to explain.
A host is indeed another computer that is hosting the virtual machines that you run.
In other words, you got it correct, a different computer with different hardware.
Note that for a virtual machine almost all of the hardware it sees is virtual, so using another host doesn't really change much as far as the virtual machine cares.
This is one of the magnificent things about virtual machines, they are very easy to move to different hardware.
There's an exception when it comes to the CPU, the virtual machine does see the CPU directly, so if there's a big change then the VM might notice that.
Even in this area there are ways to mask away specific features of the CPU so that you can make big changes look smaller.
While this feature can be used in Fusion, it isn't really exposed, this "CPU masking" is something that is being used by the product like vSphere that are used in the datacenter.
Anyways.. that's a bit off topic.
There are 2 documents here that might be interesting to read:
A Beginner's Guide to VMware Fusion | VMware Communities
and
Frequently Asked Questions about VMware Fusion , in particular the part on Virtual Hardware
--
Wil