They are the same concepts, apart from the NULL value returned.
See below:
declare @table1 table( col1 int, col2 int );
insert into @table1 select 1, 11 union all select 2, 22;
declare @table2 table ( col1 int, col2 int );
insert into @table2 select 10, 101 union all select 2, 202;
select
t1.*,
t2.*
from @table1 t1
full outer join @table2 t2 on t1.col1 = t2.col1
order by t1.col1, t2.col1;
/* full outer join
col1 col2 col1 col2
----------- ----------- ----------- -----------
NULL NULL 10 101
1 11 NULL NULL
2 22 2 202
*/
select
t1.*,
t2.*
from @table1 t1
cross join @table2 t2
order by t1.col1, t2.col1;
/* cross join
col1 col2 col1 col2
----------- ----------- ----------- -----------
1 11 2 202
1 11 10 101
2 22 2 202
2 22 10 101
*/