Cartesian product

Hi Friends,

Why the below query making Cartesian product?

Select t3.*
from siebel.s_org_ext t1,siebel.s_party t2,siebel.s_postn t3,siebel.s_accnt_postn t4
where
t2.row_id = t1.par_row_id AND
t4.ou_ext_id = t2.row_id  AND
t4.position_id = t3.row_id  OR
t3.name = 'DEV W1'  OR
t3.name  = 'ERM AnonUser '   ;

Please could you share me more about when and how the Cartesian product made?