(1) Short for transistor-transistor logic, a common type of digital circuit in which the output is derived from two transistors. The first semiconductors using TTL were developed by Texas Instruments in 1965. The term is commonly used to describe any system based on digital circuitry, as in TTL monitor.
(3) Short for through-the-lens it is a name for the LCD screen on a digital camera that shows what is projected onto the sensor by the lens. This is an alternate to using the optical or electronic viewfinder. Also called a TTL viewfinder.