OSPF Type 3 LSA
When deploying OSPF, the Type 3 LSAs or Summary LSAs are a a type of LSA that is generated by area border routers (ABRs). Type 3 LSAs are used to provide a "summary" of all of the routes that are found in a particular area, and to advertise them into another area. The following diagram describes this:
As you can see, the Type 1 LSA that is generated by R1 in Area 2 is relayed to area 0 via the R2 ABR as a Type 3 summary LSA. The R3 ABR relays this LSA into Area 51 also as a Type 3 summary LSA.