Forth - I think thats clear 馃槈 a battle cry...
And Eorlingas means "Sons of Eorl" - Eorl was the first King of Rohan and he's quite important for the Rohirrim. He was also the one who tamed the first of the Mearas after his father was killed by one.
So the Rohirrim call themselves Eorlingas in general - sometimes also Helmingas, Helm being the ninth king and last king of the First Line - he also gave his name for Helm's Deep.