( ( ( The point ) ( where ( ( these ( two ( air masses ) ) ) meet ) ) ) ( ( is ( called ( a front ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (NN point)) (SBAR (WHADVP (WRB where)) (S (NP (DT these) (CD two) (NN air) (NNS masses)) (VP (VBP meet))))) (VP (VBZ is) (VP (VBN called) (NP (DT a) (NN front)))) (. .)))
The point where these two air masses meet is called a front.
(ROOT (S (PP (IN In) (NP (NN weather) (NNS terms))) (, ,) (NP (NP (DT the) (NN boundary)) (PP (IN between) (NP (CD two) (NN air) (NNS masses)))) (VP (VBZ is) (VP (VBN called) (NP (NN front)))) (. .)))
In weather terms, the boundary between two air masses is called front.