Such coupling may be achieved by a wire, resistor, or common terminal, such as a binding post or metallic bonding.
The provision of DC bias only occurs in a group of circuits that forms a single unit, such as an op-amp.
This technique is used by default in circuits like IC op-amps, since large coupling capacitors cannot be fabricated on-chip.
That said, some discrete circuits (such as power amplifiers) also employ direct coupling to cut cost and improve low frequency performance.
All applications that require monitoring of slowly changing signals (such as those from thermistors, thermocouples, strain gages, etc.)