Complete fertilizers or balanced fertilizers are so-called because of their amounts of nitrogen, phosphorus, and potassium. A fertilizer listed as "15-15-15," for instance, would be a balanced fertilizer because of the equal proportions. One listed as "24-6-10" would not be considered complete, but referred to as an "incomplete fertilizer."
An incomplete fertilizer is not necessarily inferior to a complete fertilizer. Identifying better fertilizer depends on the circumstances. If your soil already had an excess of one of the three nutrients in NPK, you could actually be harming some of your plants by adding more of it to the soil. That is precisely what you would be doing, (inadvertently) by using a complete fertilizer. This is why it is important to have your soil tested. Otherwise, whenever you add anything to your soil, the effect (whether positive or negative) is left to chance.