On broadcast networks like Ethernet, every router forming adjacencies with every other router creates too much overhead. OSPF elects special routers:
Designated Router (DR): All routers form adjacencies only with the DR. The DR advertises the network's LSA.
Backup Designated Router (BDR): Stands ready if the DR fails. Routers also form adjacencies with the BDR.
DROther: All other routers. They reach -Way state with each other but don't exchange LSAs directly.
On a network with routers, instead of adjacencies, you have (each router with DR and BDR). This scales much better.