CTC Blank
The special label in Connectionist Temporal Classification used for time steps that do not emit an output symbol in the collapsed transcription.
CTC learns from sequences without requiring a pre-aligned target token for every input frame. The blank symbol expands the alignment space so that non-emitting steps and repeated labels can be represented; the collapse operation later removes blanks and merges appropriate repeats.
Blank is not simply a “silence class.” It belongs to the alignment mechanism and directly affects decoding. Whisper's speech-recognition architecture provides a useful contrast because it uses a different sequence-generation formulation.