tremolo?

[Nir Bar-Zvi]

i had my Italian speaking parents translate Corbetta's 1639 book (very thin introduction), and he spoke of him putting the sign "T" for tremolo in the pieces which are part tab part alfabeto, without elaborating about what he meant.

i wonder, what tremolo technique speaking of? was the tremolo i know from modern guitar present during those days? or does that mean something else?