In the poetic, the aisling would come to the poet in the form of a female (called Spéirbhean- pronounced Spare-van or Spare-ven, which means 'heavenly woman') wraith-like in appearance (can be old or young) and would lament on the state of Ireland at the time, predict a brighter future for Eire dependent upon whatever she was advising at the time.
The Aisling in dream/vision work is also part of a meditative state used by many Gaelic witchy type folks.. it is the writing down or oral description of a vision in the meditative state.. the form itself is usually poetic in nature or in story-form (which is the way of the Seannachi).
I love the movie, "The Secret of Kells". The female character is called Aisling and if you know your Irish history, you are able to recognize this as a title as well as a name.
This Aisling is one of the Tuatha De Danaan, a race of people who have become minimized and marginalized through history to resemble small creatures now called "fairies" (something which annoys a great number of us).
Many of us follow a tradition that believes we are descendants of this race of people and have a strong connection to the land and magics because of our genetic memory. It is also said that as the veil thins, we are more likely to have this experience, if we are open to it.
To have an aisling experience is very profound.
Are you open to an aisling experience?
Here is Aisling's song from the movie. Pangur Ban is a poem from the 9th century, found in the margins of a monk's book. It is said to be about his cat. There is a dispute as to the meaning of the name. For the purposes of the movie, the assumption is that it means "white cat", but etymological research says otherwise. Regardless, the song is beautiful, as is the imagery. The lyrics are profound. Enjoy!