Important definitions in SharePoint
Site Column:
A site column also known as a field,is a reusable column definition,or template that can be assigned to multiple lists or content type definitions in SharePoint. Site columns are reusable and help ensure the consistency of metadata across sites and lists. The SharePoint object model uses the class SPField to represent a site column. Also known as column template or field.
Content type:
A content type is a collection of Metadata(columns) and property settings that describes the content.
This can include fields that are associated with the content type that can be displayed as columns in the list or document library.
Site Definition:
SharePoint provides a Template architecture that allows you to create a definition
of a site and to use this definition as the template from which to create new sites .
The site definition defines the components that make up a site,such as the navigational structure, the welcome page, Web Parts that appear on provisioned pages, and the document libraries and lists that are activated upon site creation.
A site definition provides basic blue print of a site,what lists it features,the default navigation structure etc.A site definition involves a set of XML,Aspx, and other files on the front end web server.
Site Template:
A site template is a package that contains a set of differences and changes from a base site definition. This package is stored as an .stp file, which is a CAB file that contains XML files that define the differences. The .stp filecan be downloaded and uploaded to site collections by users with appropriate
rights, meaning that .stp files have some measure of portability.
For more: http://www.dhirendrayadav.com/2010/09/site-template-vs-site-definition.html
http://www.c-sharpcorner.com/uploadfile/dhananjaycoder/site-definition-in-sharepoint/
http://www.etechplanet.com/blog/sharepoint-site-definitions.aspx
