Irish, Irish Gaelic or Gaelic is a language spoken in Ireland and (less commonly) in Northern Ireland. Irish is a Gaelic and so it is similar to Scottish Gaelic and Manx Gaelic and less so to Breton, Cornish, and Welsh.
Many people who speak Irish can understand some Scots Gaelic but not Welsh because the Celtic languages are divided into two groups. One group is called the p-Celtic languages, and the other is called the q-Celtic languages. Irish and Scots Gaelic are q-Celtic languages, and Welsh is a p-Celtic language.