Runic is literacy in an angular carved script — the letterforms of a tradition that grew up around chisel, knife and axe rather than pen and ink, and whose strokes are straight and cross-grained because that is what wood and stone will take. It is read on memorial stones, boundary markers, weapon hilts, roof beams, and the incised staves passed between people who have no parchment.
Like any script, it is a writing system rather than a language: a character needs both Runic and the relevant Language to read anything written in it, and the same runic alphabet may carry several unrelated tongues. Runic is normally learned from one’s own tradition and, in cultures that use it, is far more widely held than pen literacy — a smith or a shipwright may cut a competent inscription without ever having held a quill.
Scribing and reading follow the ordinary rules for scripts. Two things distinguish this one in practice: carved work is slow, so a runic inscription is short and chosen with care; and it is durable, so the runes a character finds are frequently much older than anyone still living, in an idiom that the reader’s own Language skill may no longer entirely cover.