"Women of Ireland" was originally a poem written by Peadar O Doimin in the 18th century, later put to music by Sean O' Riada. It's a tribute to the women of Ireland who supported the independance movement. There have been many versions of that song and that tune, including by The Chieftains (which can be heard on the soundtrack of Barry Lyndon), Mike Oldfield, and more recently Nolwenn Leroy. Other versions include "Words", by the Christians, and "So Many Things" by Sarah Brightman.
Here's the gaelic text and the english translation:
http://lyricstranslate.com/en/mna-na-heireann-women-ireland.html