Any Idea What This Is? skin bump on a miniature poodle

My daughter's 11 year old miniature poodle has a few skin tag like growths.  I noticed one, by feel, on her back a week or so ago and it seems to have gotten bigger the last few days.  Today I felt that it was bigger still and, when I gently parted her hair to get a look at it, pus started coming out.  It was a plug of kinda hard pus and a little more pus came out after, with very gentle squeezing.  After it came out, there was a hole in the middle of it and it got pretty red (it was skin coloured before I squeezed).  I'll call the vet Tuesday, but does anyone have any idea what it might be?  She hasn't been anywhere outside except the rear of the condo the last several months.  Here it is in all it's glory:



I'm glad my fingernails are relatively clean...

If she were an outdoor dog I would say she got stuck with a thorn or sticker.  As an indoor dog, perhaps it is an ingrown hair.

There was a hair sticking out and I pulled it out.  A couple of small hairs came out with the follicle and it had a little blood on it.  I've cleaned it and I'll keep an eye on it.  She's due for a vet visit anyway as I'd like to get her blood work done, so at least the timing's good.

when i had the whippet as she got older she got sebaceous cysts, it sounds similar. Got full of pus, expressed easily, very nasty smelling. I want to say the vet said it was just a getting-older thing.

Sure looks to be an ingrown hair to me. My wife and I have raised Persian cats for the last twenty years and I have seen them as you describe.
Also we had one cat with a hard lump, took him to the vet thinking it was possibly a cancer... what it was, when he opened it up. Was an ingrown hair, really long all coiled up , strangest thing I have seen.
Have your vet check things out. Always better to have a professional opinion.  

almost looks like what some tick bites look like after the tic is gone.

Thomas, I'm prone to ingrown hairs and I've had that happen to me.  The fact that there was a hair right in the centre and two smaller ones came out with it (that weren't visible) leads me to think that's what it is.   I'll keep an eye on it but she's due to see the vet anyway.

Shawn, that was my first thought, but she's only been out in a small yard and I felt it grow over a couple of weeks.  It also didn't look like that until it popped.  Her hair's short and we'd notice a tick on her pretty much for sure.  It's definitely something to be aware of.

I have the same issue with my toy poodle.  What was the outcome of this? What did the vet say?