Bit stuffing

Note 1: Stuffed bits should not be confused with overhead bits.

Note 2: In data transmission, bit stuffing is used for various purposes, such as for synchronizing bit streams that do not necessarily have the same or rationally related bit rates, or to fill buffers or frames. The location of the stuffing bits is communicated to the receiving end of the data link, where these extra bits are removed to return the bit streams to their original bit rates or form. Bit stuffing may be used to synchronize several channels before multiplexing or to rate-match two single channels to each other. Synonym positive justification.

Source: from Federal Standard 1037C and from MIL-STD-188