What does “positive logic” mean in reference to logic devices?

In digital electronics, "positive logic" simply means that the higher voltage level is interpreted as a binary 1, and the lower voltage level is interpreted as a binary 0. This is the standard convention most people are familiar with when working with typical TTL or CMOS logic families. In contrast, "negative logic" assigns the binary 1 to the lower voltage level and the binary 0 to the higher voltage level. Positive logic does not mean the system is restricted only to positive voltages, nor does it refer to noise immunity or a circuit's physical "true" condition.