Ifín is one of the forfeda

Forfeda

The Forfeda are the "additional" letters of the Ogham alphabet, beyond the basic inventory of twenty signs. The most important of these are five forfeda which were arranged in their own aicme or class, and were clearly invented in the Old Irish period, several centuries after the peak of Ogham usage...

, the "additional" letters of the Ogham

Ogham

Ogham is an Early Medieval alphabet used primarily to write the Old Irish language, and occasionally the Brythonic language. Ogham is sometimes called the "Celtic Tree Alphabet", based on a High Medieval Bríatharogam tradition ascribing names of trees to the individual letters.There are roughly...

 alphabet. Its sound value
according to the Auraicept na n-Éces

Auraicept na n-Éces

Auraicept na n-Éces is claimed as a 7th century work of Irish grammarians, written by a scholar named Longarad....

, De dúilib feda and In Lebor Ogaim

In Lebor Ogaim

In Lebor Ogaim , also known as the Ogam Tract, is an Old Irish treatise on the ogham alphabet. It is preserved in R.I.A. MS 23 P 12 308-314 , T.C.D. H.3.18, 26.1-35.28 and National Library of Ireland MS G53 1-22 , and fragments in British Library Add. 4783...

, are io, ía, and ia, respectively.
The Auraincept glosses the name according to the "arboreal" tradition as spinan no ispin "gooseberry

Gooseberry

The gooseberry or ; Ribes uva-crispa, syn. R. grossularia) is a species of Ribes, native to Europe, northwestern Africa and southwestern Asia...

 or thorn

Thorns, spines, and prickles

In botanical morphology, thorns, spines, and prickles are hard structures with sharp, or at least pointed, ends. In spite of this common feature, they differ in their growth and development on the plant; they are modified versions of different plant organs, stems, stipules, leaf veins, or hairs...

".
The letter's invention dates to the Old Irish period, several centuries after the peak of Ogham usage. Since the Ogham alphabet dates to the Primitive Irish period, it had not sign for [p] in its original form. Ifín may originally have been added as a letter expressing [p], called Pín (probably influenced by Latin pinus). Due to the "schematicism of later Ogamists" (McManus 1988:167), who insisted on treating the five primary forfeda as vowels, [p] had again to be expressed as a modification of [b], called Peithe, after Beithe, also called beithe bog "soft beithe" or, tautologically, peithbog, and the earlier letter designed to express p was renamed to i-phín, and considered as expressing an i- diphthong.

Unicode

Both Ifín and Peith have 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...

allocations:

• Ifín U+1698
• Peith U+169A