An "aisling" is a type of Irish poem that tells a story about a dream or vision that a poet had. The word "aisling" actually means "dream" in Irish!
These poems became very popular in Ireland during a time when the country was under British rule, and the Irish people were struggling to keep their language and culture alive. The poems often included references to Irish mythology and history, and they often featured a woman who represented Ireland, called "Eire" or "Erin" in the poem.
In the poems, the poet often dreams that he meets this woman, who is dressed in green and gold, the colors of Ireland. She tells him about all the struggles that the Irish people are facing and encourages him to fight for their freedom.
So, an "aisling" is a special kind of Irish poem that tells a story about a dream or vision that a poet had, often featuring a woman who represents Ireland and encourages the poet to fight for Irish freedom.