“Black box” can refer literally to recording equipment and figuratively to an opaque system whose internal operation is not visible or understood. This guide focuses on the documented opaque-system sense without asserting unsupported origin chronology.
ReviewedEvidence1 sourceSectionPhrases & Idioms
Quick answer
A “black box” is an opaque system or process whose inputs and outputs may be known even when its internal workings are not visible or understood.
Key details
Canonical Formblack box
Core Meaninga system or process whose internal workings are hidden, inaccessible, secret, or difficult to understand even though inputs and outputs can be observed
Further guidance
History Boundary
Current dictionary-supported meaning is published without claiming an exact inventor, coinage date, or absolute first use.
Meaning
a system or process whose internal workings are hidden, inaccessible, secret, or difficult to understand even though inputs and outputs can be observed
Usage Boundary
Do not assume the figurative opaque-system sense whenever the words appear; aviation and other technical contexts also use black box for recording equipment.
Sources and evidence
Sources are shown with the role they play in this guide. Historical or style-sensitive claims are kept within the evidence boundary described above.
“Behind closed doors” describes something done privately, secretly, or without public observation. The page distinguishes that current meaning from any unsupported story about the phrase’s exact origin.
“Caught red-handed” means discovered in the act of doing something wrong or illegal. The expression is stronger than saying someone is merely suspected, because it centers on being found during the wrongdoing.
“Fine print” refers to small-print terms or details that may contain important conditions; Cambridge notes that “small print” is the usual UK expression. The guide stays with current documented meaning and does not add unsupported origin chronology.
“Hear It Through the Grapevine” means to learn information through an unofficial, informal chain of people. This guide publishes the current dictionary-supported idiomatic meaning and keeps exact origin, inventor, coinage, and absolute first-use claims unpublished without chronology-grade evidence.
“The inside scoop” means information that is not generally available to everyone, especially privileged or behind-the-scenes information. Merriam-Webster records “scoop” in the information sense and uses “inside scoop” in its current language examples and related editorial material.
“Keep something under wraps” means to keep it secret or concealed from public knowledge. This guide explains the established current sense without promoting an unsupported origin story.
To keep your cards close to your chest is to keep your plans or intentions secret. The metaphor is transparently connected with concealing a hand of playing cards, but exact dating is uncertain. The reviewed history source explicitly warns that popular 1860s-origin claims lack citations and treats mid-twentieth-century figurative evidence as the safer documentary floor.
To let the cat out of the bag is to reveal a secret, often unintentionally. Phrase Finder and Word Histories both document a 1760 London Magazine use. Popular market-swindle and cat-o’-nine-tails explanations are kept separate from that secure chronology because the reviewed evidence does not directly establish either as the phrase’s origin.
