Why is every first episode called pilot?

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Tags

1. #project
2. #network
3. #series
4. #development
5. #serving
6. #episode
7. #applies
8. #pilot
9. #experiment
10. #executives
11. #meaning
12. #going
13. #model
14. #future
15. #tentative
16. #decide
17. #whether
18. #might