( ( ( Air ( -LRB- ( atmospheric ( -RRB- pressure ) ) ) ) ( at ( any location ) ) ) ( ( is ( ( the pressure ) ( exerted ( by ( ( the weight ) ( of ( ( the air ) ( overlying ( that site ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (NNP Air) (-LRB- -LRB-) (NNP atmospheric) (-RRB- -RRB-) (NN pressure)) (PP (IN at) (NP (DT any) (NN location)))) (VP (VBZ is) (NP (NP (DT the) (NN pressure)) (VP (VBN exerted) (PP (IN by) (NP (NP (DT the) (NN weight)) (PP (IN of) (NP (NP (DT the) (NN air)) (VP (VBG overlying) (NP (DT that) (NN site)))))))))) (. .)))
Air (atmospheric) pressure at any location is the pressure exerted by the weight of the air overlying that site.
(ROOT (S (PP (IN At) (NP (NP (DT the) (NN earth) (POS 's)) (NN surface))) (, ,) (NP (NP (DT the) (NN air) (NN pressure)) (VP (VBN exerted) (PP (IN on) (NP (PRP you))))) (VP (VBZ is) (NP (NP (DT a) (NN result)) (PP (IN of) (NP (NP (DT the) (NN weight)) (PP (IN of) (NP (NP (NN air)) (PP (IN above) (NP (PRP you))))))))) (. .)))