Is a Site Column related to a web or site collection

Question

just going through some slides for SharePoint 2010 Developer Certification slides and it says Site Columns are related to web, but I thought they are created on site collection level, can someone explain the concept of it for me please.

Answer 1

TimeToThine,

Introduction to Columns

Specially look at the Column Scope section, which says Site Columns scope is same as Content Types...!

Also like content types, site columns are available to all the child sites of the site on which they are defined.

At the site level, the site column collection contains definitions for each site column defined on the site, whether or not it has been added to a content type or list on that site.

I hope this explains...