Avian influenza — known informally as avian flu or bird flu — refers to "influenza caused by viruses adapted to birds." The type with the greatest risk is highly pathogenic avian influenza (HPAI).
"Bird flu" is a phrase similar to "swine flu," "dog flu," "horse flu," or "human flu" in that it refers to an illness caused by any of many different strains of influenza viruses that have adapted to a specific host. All known viruses that cause influenza in birds belong to the species influenza A virus. All subtypes (but not all strains of all subtypes) of influenza A virus are adapted to birds, which is why for many purposes avian flu virus is the influenza A virus. (Note, however, that the "A" does not stand for "avian").
Adaptation is not exclusive. Being adapted toward a particular species does not preclude adaptations, or partial adaptations, toward infecting different species. In this way, strains of influenza viruses are adapted to multiple species, though may be preferential toward a particular host. For example, viruses responsible for influenza pandemics are adapted to both humans and birds. Recent influenza research into the genes of the Spanish flu virus shows it to have genes adapted to both birds and humans, with more of its genes from birds than less deadly later pandemic strains.
Tomorrow's coming 'round
A hair-pin curve in the road
She's got a run in her stocking
And she's missing the heel of her shoe
Got up this morning rolled out of bed
I spilled a diet coke
Called my mother said, "Hi"
What I meant to say was, "Why is your life a joke?"
Then, I went down to that ugly bar and
I clicked my heels three times just like you said
And I climbed that road to your empty house
The anticipation was a turn on
But you let me down
'Coz, I stood on that empty street alone
I said, "I'm ready for my close up now, Mr. Demille"
I waited for the light, but it never shone
Well I wonder what you do with that expensive piece of land
That overlooks a billion years of history
I have a sneaking suspicion, you will never understand
Hey maybe I'll see you down by the Rocky and Bullwinkle
And we can talk to that charlatan psychic
And she can paint a prettier picture of your future
'Coz that day in my life, that day in my life
I dreamt tomorrow, had a prettier face
I dreamt tomorrow, would have better things to say
Than, "You look like shit, what's your problem, bitch?
You're legs feel like sandpaper, you can't do anything right"
'Coz that day, never should have taken place
'Coz this day, in my life still cannot explain
Why I listened in the first place to you?
Oh yeah, something else
I hope one day you call up your father
And you have the guts to tell him, how he hurt you
And he made you hurt another