"Jack" Natural Recordings by Native Speakers
A jack is a noun that refers to a person's name, typically an informal or colloquial term.
A jack-in-a-box is a type of toy consisting of a box with a spring-loaded figure of a clown or other character inside. When the box is lifted or opened, the figure suddenly pops out, often with a loud noise and a startling motion, causing surprise and delight, especially in children. The phrase is also sometimes used metaphorically to describe someone or something that bursts into prominence or attention unexpectedly.
A jack-in-the-box is a toy that consists of a box with a spring-loaded figure, typically a clown or other character, that suddenly pops up and out of the box when a spring is released or a lever is pressed. This is often used to describe a surprise or a sudden, unexpected event.
To jack-knife means to fold or bend something, usually a vehicle, in half, often to the point where it is perpendicular to its original direction. In the context of transportation, a jack-knifed vehicle refers to a large vehicle, such as a truck or bus, that has suddenly turned to its side or folded in upon itself, often as a result of sudden braking or loss of control, blocking traffic and potentially causing accidents or injuries.