Features could be said to be the most ground-breaking addition to this version of WSS. A SharePoint Feature is a collection of SharePoint elements that can help a user accomplish a particular goal or task. Features can also be described as logical groups of elements that together serve a common purpose. How many times have you had a need to add a chunk of functionality to an existing server farm, web application, Site Collection, or site, such as an event handler, custom navigation, or maybe even a set of lists or document libraries all at once? An example is a set of lists and libraries combined with workflow and custom navigation that contain the functionality required to enable a certain business process to function within SharePoint. Features make it possible to activate or deactivate functionality in the course of a deployment, and administrators can easily transform the template or definition of a site simply by toggling a particular Feature on or off in the user interface. As noted in the SDK, Features provide the following capabilities:
Scoping semantics for determining where custom code runs
Pluggable behavior for installing or uninstalling Features within a deployment
Pluggable behavior for activating or deactivating Features at a given scope
A scoped property bag for storing data required by a Feature within its scope
The basis of a unified framework for distributed deployment of WSS v3 solutions
A Feature is implemented by adding a subfolder containing a ...