What is the term for transmitting data one bit at a time?

The term that describes transmitting data one bit at a time is "serial." In a serial communication mode, bits are sent sequentially over a single channel. This method contrasts with parallel transmission, where multiple bits are sent simultaneously across multiple channels. Serial transmission is commonly utilized in various communication protocols due to its simplicity and lower cost, leading to less complexity in wiring and reduced opportunities for interference that could occur with multiple lines carrying bits at the same time.

In contrast, synchronous and asynchronous communication refer to the timing of data transmission rather than the number of bits sent at once. Synchronous communication relies on a common clock signal to coordinate the timing of transmissions, while asynchronous communication does not, allowing for data to be sent independently of a clock signal. However, neither directly describes the method of sending data bit-by-bit as "serial" does.