what does mean this statement?

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C#

LINQ

hello . in a code setion is see following code:

public static void Delete<T>(object primaryKey) where T : class
       {
           using (MainDataContext context = new MainDataContext())
           {

               MetaDataMember id = context.Mapping.GetTable(typeof(T)).RowType.IdentityMembers[0];
               ParameterExpression parameter = Expression.Parameter(typeof(T), "item");
               T entity = context.GetTable<T>().Single<T>(Expression.Lambda<Func<T, bool>>(Expression.Equal(Expression.Property(parameter, id.Member.Name), Expression.Constant(primaryKey)), parameter));
               context.GetTable<T>().DeleteOnSubmit(entity);

           }
       }

i can't understandit. please guide me.
edited : MainDataContext is generated by LinqToSql tools in visual studio 2010