What's considered an "asset" in the Ruby on Rails universe?
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Are *user generated files*, such as images uploaded by the user, considered **assets**? Where should they be stored in the standard file structure of a Rails project? Should they be kept clear of any asset related directories like:

* app/**assets**
* lib/**assets**
* public/**assets**

Relevant: [The Asset Pipeline](http://guides.rubyonrails.org/asset_pipeline.html)