Border Gateway Protocol
It’s signaling other BGP neighbors about networks with some rules for them. Also BGP is path vector protocol, and it’s not necessary to learn all topology like OSPF/ISIS. In Internet we don’t need it. BGP can pass through many “families” of routes like l2vpn, l3vpn, ipv4 and ipv6. Also you can create bgp mpls network with some redudnancy and stuff, so, it is usefull within AS and between Internet routers 
hahaha… i think that’s the easiest post that i’ve ever seen haha