Basal tears is a term used to distinguish the quality and composition of (a) the protective tear film which normally covers the surface of the eye at all times from (b) the reflex tears secreted as a result of eye irritation (wind, something in the eye etc) or those triggered by emotion.
When you have chronic dry eye it is useful to understand that the "normal" tear film (basal tears) has unique qualities to protect and nourish the corneal surface which reflex or emotional tears cannot replicate. Ever wonder why your eyes hurt more after crying? Those tears are more watery. In effect the good stuff - in the basal tears - is getting washes/diluted right out of your eyes. Some dry eye patients try to "make" their eyes wet by stimulating reflex tears; although these may make the eyes temporarily wet, they can never really replace basal tears.
The goal of the dry eye patient is not simply to make their eyes wetter but to improve the constant tear film - that is, basal tears - to the extent possible, for the better protection and nourishment of their corneas.