Greetings,
I suspect that this is going to be rather short, but I think it will supply some useful information of interest. The question would seem to have a relatively simple answer, however there is some contention with regard to the use of terms here, and it is this which will be discussed in the following. I am going to be horribly biased with regard to this and focus on the use of the single sword in this discussion.
A ward is a position from which an attack or defense is launched. I think this is the best definition of what a ward is that I can find. A more in-depth definition of this would also include that this is a position which the combatant moves through from one action to another. What this means is that a set of actions might look like this: Ward - attack - ward - defense - ward - attack, and so forth. What is important is this is not a "guard".
A guard is a position in which one line is closed, thus the fencer is defended along that line due to being ...
The rest of this article can be found in Un-Blogged: A Fencer's Ramblings by Henry Walker, which is available in paperback from:
Amazon: https://www.amazon.com/Blogged-Ramblings-Henry-Leigh-Walker/dp/098764470X
Booktopia: https://www.booktopia.com.au/un-blogged-henry-leigh-walker/book/9780987644701.html
Among other places...
It is also available in electronic format (pdf) from: https://buy.stripe.com/fZecP419c7CB9VKeUV
... or direct from the author.