When one lies on their stomach with their hands directly at their sides and with their head pointed downwards. This is done for fun, and the point is to come up with creative places to do it, such as on top of a chimney or over public restroom stall(s). Pictures of one planking make ideal profile pictures.
Q: That kid is just randomly lying flat like a pencil on top of that diving board while his friend is taking a picture of him, what is going on?
A: That kid on the diving board is planking.
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