What does it mean to say that a framework “scales well”?

Question

When reading about frameworks (.net. ruby on rails, django, spring, etc.), I keep seeing so and so does or doesn\'t scale well.

What does it mean when someone says that

Answer 1

If a framework or an application scales well, it means that it can handle larger loads. As your site becomes more popular with more visitors and more hits per day, a framework that scales well will handle the larger load the same as it handles a smaller load. A framework that scales well will act the same when it receives 200,000 hits an hour as it does when it gets 1 hit an hour. Not only hits, but being deployed across multiple servers, possibly behind load balancing, possibly with several different database servers. A framework that scales well can handle these increasing demands well.

For instance, twitter exploded almost overnight last year. It was developed using Ruby On Rails, and it was hotly featured in the ongoing debate on whether Rails scales well or not.