A situation in asynchronous programming where multiple nested callback functions create deeply indented, hard-to-read code that becomes difficult to maintain and debug. This typically occurs when handling sequential asynchronous operations.
The term 'callback' comes from the practice of calling back to a provided function, while 'hell' is used colloquially to describe an unpleasant or chaotic situation. The phrase emerged in the JavaScript community as Node.js popularized callback-based asynchronous programming.
Callback hell is like trying to give directions where each step depends on the previous one: 'Go to the store, and when you get there, buy milk, and when you buy milk, check if they have cookies, and if they do...' - it becomes an impossible nested maze! This is why promises and async/await were invented.
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