When distilling there are 'cuts' to be made to ensure you get safe and desirable tasting spirit. Below explains the cuts;
The first distillate or condensed vapour from the still which can contain undesirable elements. This could contain methanol as well which should not be consumed.
The first part of the collected alcohol which can be used in blending. These contain more alcohol soluble compounds and often have fruity/ester character.
Any heads not used in blending can be added to future runs to improve yield.
The main distillate or condensed steam collected from the still. The hearts or body comes off between the "heads" and "tails" and is the most desired part of the distillate as it will be the part that tastes the best and is of the best quality.
The last portion of alcohol that is produced from most stills. This portion contains heavier alcohols, a much higher percentage of water and other unwanted by-products which are more water soluble.
Some stills like the Turbo 500, by design, do not produce "Tails", this is normally used in a Pot Still setup.