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 components of a basic drum kit in 90 seconds Learn components of a basic drum kit in 90 seconds
Learn Japanese vocabulary in 90 seconds - Theme: Animals! Learn Japanese vocabulary in 90 seconds - Theme: Animals!
Learn about Japanese Holidays in 90 seconds! Learn about Japanese Holidays in 90 seconds!
Learn what the 12-hue color wheel is in 90 seconds Learn what the 12-hue color wheel is in 90 seconds