An el rune is a low tier rune that can be socketed into armor and weapons. You can obtain an el rune from normal countess. You can get an el rune from the normal hellforge quest.
An el rune requires level 11 to use.
Horadric cube recipes with el runes
transmute 3 el runes to create an eld rune
transmute low quality armor, an el rune, and a chipped gem to create normal quality armor of the same type