What are event receivers or event Handlers in SharePoint?
Ans. Event Receivers or Event handlers are created to handle the basic actions or events against an item,list\library, a web or a site. There are two kinds of events in sharepoint.
Synchronous Events: Like Itemadding (not added yet), Uploading (document not uploaded yet) etc.
Asynchronous Events: ItemAdded (after item is added), Uploaded(after a document is uploaded)
Events receivers can be written to override an event for e.g. ItemAdded event to change the name of an Item once it is added.
You will normally, find it under C:\Program Files\Common Files\ shared\web server extensions\12\bin.