As for the title of Janet Harbison's influential 1996 paper, it comes of splitting Irish musicians who play the harp -- specifically the Irish harp -- into three categories. I am going to word this my way instead of quoting Harbison directly.

1. Harpist: literate in the tradition of classical, academic, institutionalized, written/printed music. An example would be the late Sanchia Pielou, Irish by birth, and one of the founders of the BBC Scottish Symphony Orchestra. Pielou is relevant to this Irish-music thread because, before leaving Ireland for Scotland, she was one of the more advanced harp students of Caroline Townsend in Dublin. Pielou remained anchored with her classical-music credentials: besides the Orchestra, she devoted her teaching career to what used to be called the Royal Scottish Academy of Music and Drama in Glasgow, where she was made a Fellow. There Pielou taught both the "clairsach," the Irish harp, and the "cruit," which is the Gaelic word inclusive enough to cover both Celtic harps and the big concert harps.

2. Harper differs from Harpist, according to Janet Harbison, in that Harpers focus on traditional Irish music in session playing, and they apply themselves to the dance music repertoire from which, in another century, they were more often than not excluded. The trailblazers here include Máire Ní Chatasaigh.

3. Finally, the Harpee! Invariably, she sings, she has had voice training, and instrumentally she is more of a three-chord wonder, using the harp to accompany her songs. From the teaching studio of Caroline Townsend (would she be limited to any one of these three categories, or would she be a combination of two or three of them?), the sterling example would be an entire generation of daughters of Seán Ó Séaghdha, most if not all of whom studied with Ms. Townsend in Dublin when this pathfinder of the Irish harp was in her seventies. From youngest to oldest, those Ní Shé sisters are, again:
Nuala, born 1923, possibly still living because I cannot locate anything about her death. Married; seems to have stayed out of music entirely once she had her own family/household.
Nuala's older sisters are all deceased now:
Niamh, performed with her sisters on the cabaret circuit until she married, then gave up music and taught home economics.
Róisín Uí Thuama, the widow of actor Seamus Ó Tuama.
Nessa Doran, who after her marriage gave up the musical performances in public, and devoted herself to Irish Gaelic philology and scholarship;
and the first-born Máirín, herself the teacher of Janet Harbison, of whom Harbison writes that she learned the harp from Caroline Townsend without ever learning to read music herself.