Nitrogen, Phosphorus, and Potassium (N,P,K) are what the numbers refer to. They are always listed in this order. It is the percentage within that package of each component. Phosphorus (P), the middle number, is very effective at establishing growth below ground, in the form of healthy root systems. It is also the component most responsible for flower blooms and fruit production.
You’ll notice that fertilizers designed for flower production, or starter-type fertilizers for your lawn, have a high middle number. For promoting good fruit or flower production, look for a middle number that is higher than the first. Otherwise, your plants will be stimulated to put out lots of nice green foliage, likely at the expense of fruit or flower production.
Instead, you want the energy and nutrition of the plant to go towards the desired result, flowers or fruit, so a higher middle number is a more appropriate choice.