I ask in an international context, and NOT only for New York. I'd cherish a picture to visualise the definitin. For example, NY Times fails to define the word, whereas the dictionaries appear conflicting and vague. Even Straightdope's apparently catholic answer hedges with the word apparently?
2.3. [North American] Any urban or suburban area bounded by four streets
4. [countable] (North American English) the length of one side of a piece of land or group of buildings, from the place where one street crosses it to the next
NY Times only worsens my confusion: 'North-south' implies 1 mile = 20 blocks, but this differs from 'The distance between avenues'? What are 'short blocks' and 'long blocks'?
Straightdope.com: Apparently the answer to the question hinges upon which city, and within that city, what is defined as a block.