An element (number 14 in the periodicThis can be a characteristic of some signal. If the signal changes somehow, and that change repeats itself exactly over time, over and over - like a sine wave - then the signal is said to be periodic. The amount of time it takes for the signal to repeat itself is called the "period." table) that can be a semiconductorA material that, under some circumstances, can conduct electricity and, in other circumstances, cannot., making it the material of preference for circuits and micro-mechanical devices.