SQL Server Security Hierarchy
An owner is a database principal that has ownership of a particular object, giving that principal full rights to the object(including ALTER, SELECT, INSERT, UPDATE, and DELETE).  This principal can either be a database user or schema, depending on the context in which the object was created and the permissions of the principal that created the object.  In the case of no explicit object ownership, the object is owned by the related schema owner.

There is also the db_owner role which exists in each database.  Members of this role are considered to have ownership of the database and all objects within that database.  Essentially, members of the db_owner role have "sysadmin/sa" rights in that specific database.

'dbo' is a default database user that is made a member of the db_owner role.  Additionally, the 'dbo' schema is also created and used as default schema to create objects within.  This schema is owned by the 'dbo' user.

To view object ownership, you can use the following query against the DMVs:

select
    SCHEMA_NAME(s.schema_id)+'.'+OBJECT_name(o.object_id) [ObjectName]
    ,u.name [ObjectOwner]
    ,so.name [SchemaOwner]
from
    sys.objects o
    left join sys.schemas s on (o.schema_id = s.schema_id)
    left join sys.database_principals so on (s.principal_id = so.principal_id)
    left join sys.database_principals u on (o.principal_id = u.principal_id)


For more detail, you can read Aaron's link or this article from Kathi Kellenberger.