Meaning of the term 'tack' in bread making?
I am not sure there is common meaning of "tack" that makes sense in this context.  I suspect it is a typo for "tacky", but even so, tacky implies a certain amount of stickiness.

On the other hand, the outcome that is indicated is clear.  When your dough first forms, it sticks to almost anything:  the sides of the bowl, the counter, your hands, leaving a residue.  As you knead and develop the gluten in the dough, it will prefer to stick to itself, rather than these surfaces.