Antiparallel (electronics)
In electronics, two anti-parallel or inverse-parallel devices are connected in parallel but with their polarities reversed.
One example is the TRIAC, which is comparable to two thyristors connected back-to-back (in other words, reverse parallel), but on a single piece of silicon.
Two LEDs can be paired this way, so that each protects the other from reverse voltage. A series string of such pairs can be connected to AC or DC power, with an appropriate resistor. With AC, the LEDs in each pair take turns emitting light, on alternate half-cycles of supply power, greatly reducing the strobing effect to below the normal flicker fusion threshold of the human eye. Some two-color LEDs are constructed this way, with the two dies connected anti-parallel in one casing.
ESD
Antiparallel diodes are often used for ESD prevention in ICs. Different ground or supply domains at the same potential or voltage may be wired separately for isolation reasons. However, during an ESD event across the domains, you want a path for the high current to traverse. Without the antiparallel diodes in place, the voltage induced by the ESD event may result in the current following an unknown path that often leads to damage of the device. With the diodes in place the current can travel in either direction.