Probably sensitivity. The numbers probably reflect the effective concentration of antibiotic for the particular organism.
Sensitivity patterns. The less the number more effective is the antibiotic.
MIC. This number is called the minimum inhibitory concentration (or mic). It means the lowest concentration of antibiotic that inhibits the growth of the organism. In general, the lower the mic, the more sensitive the organism is to the antibiotic. There are other factors that go into choosing an antibiotic however, so choosing the antibiotic with the lowest mic is not always best.