(1) See 
A/D converter and 
application delivery controller.
(2) (
Advanced 
Data 
Connector)  See 
RDS.
(3) (
Application 
Delivery 
Controller)  An umbrella term for a variety of network devices that provide traffic management.  Load balancing, compression and caching are some of the functions of an ADC.
(4) (
Apple 
Display 
Connector)  An earlier peripheral connector from Apple that combined video display, USB and power in one cable.  Introduced in 2000 with the G4 Cubes, adapters provided VGA to ADC and DVI to ADC conversion.  Eventually, ADC gave way to DVI.