90秒で分かるRuby on RailsとかのWebフレームワークって何なの?

Webアプリケーションの開発になくてはならないWebフレームワーク。Ruby on Railsなどのフレームワークって一体どういうものなんでしょう?90秒で学んでみましょう!
Learn the difference between eye fatigue and eyestrain in 90 seconds Learn the difference between eye fatigue and eyestrain in 90 seconds
Learn Japanese vocabulary in 90 seconds - Theme: Fruit! Learn Japanese vocabulary in 90 seconds - Theme: Fruit!
Learn common Kansai-ben words in 90 seconds! Learn common Kansai-ben words in 90 seconds!
Learn Japanese vocabulary in 90 seconds - Theme: Appearance! Learn Japanese vocabulary in 90 seconds - Theme: Appearance!