A tir rune is a low tier rune that can be socketed into armor and weapons. You can cube 3 eld runes together to get a tir rune. You can also obtain a tir rune from normal countess. You can get a tir rune from the normal hellforge quest.
A tir rune requires level 13 to use.
Horadric cube recipes with tir runes
transmute 3 tir runes to create a nef rune