An abbreviation for handbook; a concise reference book containing essential information or instructions about a subject or procedure.
Abbreviated from 'handbook' by taking the first letter of 'hand' (h) and 'book' (bk), using consonant-only abbreviated notation common in technical and military writing.
Military and technical fields pioneered extreme abbreviation to save space and transmission time—HDBK became standard in specifications and manuals where every character cost money to transmit or print.
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