Indentured service, which simply means making a legal agreement to enter service (become a servant) for a defined period in exchange for a defined payment, was certainly a real thing, and those who signed agreements to engage in such service certainly included a significant number of Irish people.
While it's hard to know without seeing the thread you are referring to, it seems most likely the actual issue being discussed, or alluded to, is the question of whether indentured service, specifically in North America or the Caribbean, specifically on plantations, equated to "white slavery" – a dogwhistle topic for quite a number of groups.
This is a topic that comes up here repeatedly, and while there's always more to say, you might like to review this earlier thread, led by u/sowser, which thoroughly covers the issue, while you are waiting for fresh answers to your query.
Hi, great question!
There are a few ways that the Irish were indentured by British law in the 17th through 19th centuries. The first is through the so-called Penal Laws. It was a raft of punative, anti-Catholic laws ranging from being unable to hold office, to barring Catholic education, to not being able to own a horse worth more than £5, to the inability to refuse work if offered by a Protestant.
It is this last provision that makes poor, rural Irish Catholics de facto indentured even though they may not owe their "master" a thing. Refusal to work for a landowner could lead to beatings, prosecution under the laws and (in theory) summary execution (there are diary accounts claiming such kinds of retribution). A good source for the scope and impact of these laws is Eyewitness to Irish History by Peter B Ellis. Lots of primary sources as well as selected laws themselves really sheds light on the state of poor, rural Irish.
Usually, once a rural Irish worker was 'employed' by a landowner, they often incurred debt - real or fictional - that the landowner held. This made the worker a more de jure indentured servant and British law was quite thorough about punishing indentured servants who ran away (or "ran away"), were impudent, etc. It was often (though not always) a no-win situation.
The other way that the Irish were "indentured" was during the Cromwellian conquests. After a campaign that was punctuated with horrific atrocities, his army shipped 50,000 Irish to "the Bahamas" as essentially slaves; others were basically banished to the rough lands of the west counties, especially the Burrens, where one of Cromwell's assessors once describes as having "Not enough water to drown a man, not enough wood to hang him, and not enough soil to bury him"
However, by the time you get to the 19th century, especially in the Great Famine of the 1840s when British policies made a bad situation immeasurably worse, roughly 1/3 of the population was so desperate to leave in order not to succumb to starvation, typhus, or the other ravages of the famine, many took servant positions in England (especially London), Australia, the United States, and anywhere else that would take them (such as in Latin America).
Hope that helps, and I do hope you check out Ellis' book; there is so much to see in these primary sources that I cannot do it justice with this post. For a less thourough, though equally moving documentary, check out BBC's "Story of Ireland" hosted by Fergal Keane.