There's actually a decently detailed description of a leather cuirass found in the Táin Bó Cúalnge, this particular excerpt is taken from the recension found in the Book of Leinster, from a passage where the protagonist Cú Chulainn is readying himself for battle:

Ro gabastar a chathchriss curad taris anechtair do chotutlethar crúaid coirtchide do formna secht ndamseiched ndartada congabad dó ó thana a thaíb co tiug a oxaille. Ro bíth imbi ic díchur gaí & rend & iaernn & sleg & saiget, dáig is cumma focherdditis de & marbad de chloich nó charraic nó chongna ro chiulaitis.

Outside [his clothing] he donned his warrior's battle-girdle of tanned, hardened, stiff leather, made from the best parts of seven ox-hides of yearlings, which covered him from the thin part of his side to the thick part of his arm-pit; he used to wear it to repel spears and points and darts and lances and arrows, for they glanced from it as it they had struck against stone or rock or horn. (Translation mine)

Leather cuirasses are mentioned another time in the text, though not in such great detail. Because the poem is written in alliterative verse, the author chose to call the item chathchriss (battle-girdle) in order to maintain his alliterative meter, however the actual Old Irish word for a piece of armour covering the torso is lúirech. It should also be noted that the size of the cuirass described above is absolutely exaggerated (a piece of clothing made from seven ox-hides would be enormous), as medieval Irish narrative literature has a tendency to play fast and loose with size, distance and time for dramatic effect.

Having looked up the term, it seems to be quite vague and applied to most types of body armour regardless of the material used or overall shape of the item, judging by its use in a Middle Irish text to presumably describe a viking wearing chain mail tunic (Gall ina luírigh). This lack of specific vocabulary for different varieties of body armour perhaps speaks to its widespread absence in early medieval Irish warfare, where items as varied as boiled leather cuirasses and chain mail hauberks were so uncommon that they were simply lumped together in a single category of "armour covering the body".