Bitstream

A bitstream (or bit stream), also known as binary sequence, is a sequence of bits.

A bytestream is a sequence of bytes. Typically, each byte is from a range of 256 distinct values (octets), and so the term octet stream is sometimes used to refer to the same thing. An octet may be encoded as a sequence of 8 bits in multiple different ways (see endianness) so there is no unique and direct translation between bytestreams and bitstreams.

Bitstreams and bytestreams are used extensively in telecommunications and computing. For example, Synchronous Digital Hierarchy transports synchronous bitstreams, and transports an asynchronous bytestream.

Formally, a bytestream is a certain abstraction, a communication channel down which one entity can send a sequence of bytes to the entity on the other end. Such channel is often bidirectional, but sometimes unidirectional. In almost all instances, the channel has the property that it is reliable; i.e. exactly the same bytes emerge, in exactly the same order, at the other end.

Less formally, one can think of it as a conduit between the two entities; one entity can insert bytes into the conduit, and the other entity then receives them. This conduit can be transient or persistent.

In practice, bitstreams are not used directly to encode bytestreams; a communication channel may use a signalling method that does not directly translate to bits (for instance, by transmitting signals of multiple frequencies) and typically also encodes other information such as framing and error correction together with its data.

...
Wikipedia