Under most circumstances, the two are the same, as John says.
There is a little difference in nuance and use.
If I say 'armistice', I am implying that two armies have stopped hostilities for the purpose of discussing permanent peace terms.
If the word 'truce' is used, I tend to think of it as more temporary, even though it might indeed lead to permanent peace terms. A truce might be declared to let both armies collect their wounded. I would not use 'armistice' in that case, even though the definition is technically correct.
Also, if two people have a heated argument and decide to stop the argument for a later time, we say that they have declared a truce.
"I STILL think you're wrong."
"OK, truce. I'm tired of arguing, let's just go back home and start again later."
I would not use 'armistice' to describe that, since there are no arms involved.