To go a bit beyond what Ray mentioned, and add my reasoning.....
A full distal taper includes both the blade, and the tang. The thickest portion of the blade would be right in front of the handle scales or the guard, with the blade tapering to the point from there, and to the end of the handle.
A proper distal taper not only lightens, and makes a knife feel more balanced, it also increases overall strength of a blade. How? When a blade has proper distal taper, and you apply a lateral force to the blade, it forms an arch. What is the strongest structural design? An arch.
For example, if a lateral force is applied to a blade that is a single, given thickness throughout it's length, the force applied will seek out, and concentrate itself in/at the weakest point, generally causing breakage with much less force, and much less resilience then a blade of similar design that includes distal tapers.
When lateral force is applied to a blade with a proper distal taper, the blade forms an arch, and because of this, the force seeks to distribute itself evenly/equally along the length of the arch/blade, meaning even though the blade is generally significantly thinner and lighter then a single thickness blade of the same design, the one with the distal taper will withstand a greater force without being damaged. Of course that doesn't make is indestructible, it simply means that it will tolerate more lateral stress, and do it in a lighter weight, better balanced package then can be achieved with a blade that is a single thickness through out it's length.
Another reason I use distal tapers in nearly ever blade I produce is the fact that IF a blade/knife includes proper distal tapers, it's difficult for it to finish out "unbalanced"....that's assuming the maker doesn't do something silly like hang a huge buttcap on it.
And to be really honest, any knife that does not include distal tapers feels really "clunky" and heavy to me.