The Yr rune is a rune of the Younger Futhark

Younger Futhark

The Younger Futhark, also called Scandinavian runes, is a runic alphabet, a reduced form of the Elder Futhark, consisting of only 16 characters, in use from ca. 800 CE...

. The name yr means "yew"

Taxus baccata

Taxus baccata is a conifer native to western, central and southern Europe, northwest Africa, northern Iran and southwest Asia. It is the tree originally known as yew, though with other related trees becoming known, it may be now known as the English yew, or European yew.-Description:It is a small-...

 in Old Norse

Old Norse

Old Norse is a North Germanic language that was spoken by inhabitants of Scandinavia and inhabitants of their overseas settlements during the Viking Age, until about 1300....

.

It developed out of the Algiz

Algiz

The Algiz is part of the ancient Nordic and Anglo-Saxon runic alphabet, often equated to the modern day z, however was traditionally pronounced yr. The letter has come to symbolize many neo-pagan religions and is often worn as a pendant...

 rune as the Younger Futhark gradually began to replace the Elder Futhark

Elder Futhark

The Elder Futhark is the oldest form of the runic alphabet, used by Germanic tribes for Northwest Germanic and Migration period Germanic dialects of the 2nd to 8th centuries for inscriptions on artifacts such as jewellery, amulets, tools, weapons and runestones...

 from around the 7th century.
Its common transliteration is a small capitals  (ʀ).

Its phonological value is also the continuation of the /z/ phoneme represented by Algiz, the word-final *-z in Proto Germanic, notably the nominative desinence (PIE

Pie

A pie is a baked dish which is usually made of a pastry dough casing that covers or completely contains a filling of various sweet or savoury ingredients....

 *-s). In Proto-Norse pronounced closer to r, perhaps ɻ. Within Old Norse, the Proto-Norse phoneme collapses with /r/.

Unicode

Unicode

Unicode is a computing industry standard for the consistent encoding, representation and handling of text expressed in most of the world's writing systems...

 has "Latin Small Capital Letter R" at codepoint U+0280 . A corresponding capital letter is at U+01A6 , called "Latin Letter Yr". The rune itself is encoded at U+16E6 "Long Branch Yr".
Variants are "Short Twig Yr" at U+16E7 and "Icelandic Yr" at U+16E8 .

Note that the unrelated Anglo-Saxon calc rune ᛣ has exactly the same shape as Younger Futhark yr.