Gaafil is an Urdu word which was quite used in poetry but nowadays it's found less. Still, sometimes in songs or poems written by those well-versed in Urdu, like Gulzar, the word can be seen. The meaning of Gaafil is negligent, or even better neglectful, someone who doesn't care, heedless.
So now you know what it means when someone says Sair kar duniya ki gaafil, zindagani phir kahan.. (travel the world heedless, where will this life be there again).
Word 'Gaflat,' meaning heedlessness, or a more used for unconsciousness, also comes from Gaafil.