Keening (Caoineadh) was/is a traditional mourning at a wake, very like what you see in Palestine today.

Some women were particularly famous for their laments, and would be paid to come and keen over the body.

The caoineadh is a formal lament, sung to a particular series of tunes - Patrick Pearse has one in notation in one of his stories - and remembering the graces of the dead person, and emphasising how lost his family and all who loved him (or her, of course) will be now. The idea is to call out the grief of the mourners into full expression, so that they can cleanse their hearts of grief and not have it festering inside them.