Site Column

A site column is a reusable column definition, or template, that you can assign to multiple lists across multiple SharePoint sites. Site columns are useful if your organization wants to establish some consistent settings across lists and libraries. You can share the settings across multiple lists and libraries so that you don't have to recreate the settings each time. For example, suppose you define a site column named Customer. Users can add that column to their content types or list. This ensures that the column has the same attributes, at least to start with, wherever it appears.

When you add an item to the list or library, you fill out a form in which each column is represented by a field. Each field is labeled with the name of the column. If you provide a description for the column, the description appears below the field. You can use the description to help team members fill out the form by explaining what kind of information goes in the field.