Enabling the "Enterprise Keywords" in sharepoint list or document library.
If you are not seeing this column by default,the reason was you have been selected the blank site to create root site.
There are no way to activate this feature if you selected the blanksite.
You need to activate it through stsadm command
STSADM -o activatefeature -n TaxonomyFieldAdded -url http://myserver
before activating this feature please be make sure you activated the site featured called "SharePoint Server Enterprise Site features"