The term "chipload" refers to the thickness of a chip being removed. Before having a more complete understanding of this term, though, one must understand other things such as feed, speed and what happens at the cutting edge.
A chip, or thick material, is being removed from the part that is being machined. The thickness of the chip is directly controlled by the rotation speed of a spindle, and by the forward movement of the tool. The chipload is equal to the amount of material cut by the edge after a single revolution of the cutter. Chipload means the same thing when it comes to flute cutters, but in that case the chipload is spread equally over the quantity of flutes, which usually means half thickness with two flutes.
Any cutting process will produce heat, and the most effective way of removing this heat is to have it removed with the chip. This is possible if you have the correct chip size, which will work to both dissipate heat and to produce a more finished edge. This, of course, works on the assumption that the correct cutter has been selected for the operation, which will allow proper optimization of both speed and finish.
One should keep in mind, however, that heat is what deteriorates the cutting edge. A cool tool test can be performed after running a full sheet of nested parts, after which the cutter should be at or near room temperature.
And now on to chipload; if you want to increase the chipload, you only have to increase the feed rate, decrease the RPM and use less flutes. If you want to decrease the chipload, though, you must decrease the feed rate, increase the RPM and use more flutes.