Create a New Site Column in SharePoint 2010
SharePoint 2010 has a site column entity that allows you to reuse columns across multiple lists. When you create a new column in your list, you create a list column — meaning the column can be used only in that list. Site columns are created at the top-level of your team site and can be reused in any list or library within your entire team site, including subsites.
All columns you see in a list are technically list columns. When you add a site column to a list column, SharePoint copies your site column to the list to create the list column. A link is maintained between the list column and the site column. If you update the site column, you can opt to push your changes down to the list column.
To create a new site column that you can use in a list or library:
Choose Site Actions→Site Settings from your top-level site.
The Site Settings Page appears.
In the Galleries section, click the Site Columns link.
A list of site columns appears.
Click the Create link to create a new column.
The New Site Column page appears.
In the Column Name field, enter the name for your site column in the Name text box.
When naming your column, don’t put any spaces in the name. The spaces make it hard to use your column later for queries. Instead, type the name using proper name casing, such as entering ArtifactType. You can rename the column later to Artifact Type, but the internal name remains as ArtifactType.
Select the column type you want to use for your column by clicking a radio button next to an option in the Type of Information in This Column Is list.
You have many column type options. You also have the Managed Metadata column type.
In the Put This Site Column Into section, indicate into which group to place your column by selecting either the Existing Group or New Group radio button.
If you select the Existing Group radio button, choose a group from the drop-down list. If you choose New Group, enter a name for the group in the New Group text box.
A site column can be a member of one group.
Enter any additional column settings that may be required by your column type by selecting radio buttons in the Additional Column Settings section.
(Optional) In the Column Validation section, enter a formula to use to validate the values that are entered into this column in the Formula text box.
Your site column appears in the list of site columns.