A Screenplay (aka Script) can be defined as the written document containing sequential arrangement of scenes of a film. It contains the action (instructions regarding what happens on screen) and the dialogue. It thus says a story, not from a third person narrative (as in written fiction), but in the language of cinema.
However, many films, esp. in India, split the credit of 'script' into three parts:
1. the Story: the original storyline, not necessarily in the language of cinema
2. the Screenplay: that converts the story into a sequence of scenes (aka 'Scenario' in some European films, also in Satyajit Ray films)
3. the Dialogue: which when added to the screenplay, completes the script.
This explains why Filmfare awards each heads separately, while the Academy covers it under 'Best Screenplay'. Thus 'Best Screenplay' in Filmfare generally goes to 'structural' films like Yuva (2004), Life in a Metro (2007), Mumbai Meri Jaan (2008). Note how important the scene structures of these films are. While a Screenplay Oscar can go to a Juno(2007) which has an extremely simple structure but great dialogues.