Definition of "siblings" in /proc/cpuinfo

So, I'm looking over /proc/cpuinfo and have a question... I've read that "siblings" refers to hyperthreading, but that seems odd considering the contents of cpuinfo. Here's a part:

model name      : Intel(R) Xeon(R) CPU           E5410  @ 2.33GHz
physical id     : 0
siblings        : 4
core id         : 0
cpu cores       : 4

That almost seems to say that the CPU is a quad-core Xeon (which is correct) as well as being hyperthreaded-- each core having 4 hyperthreads. That seems wrong, though. It seems more likely that it's saying that the CPU has 4 cores and 4 hyperthreads total-- that is, depending on how one looks at it, one hyperthread per core, or, alternatively, 4 cores and no hyperthreading. Four hyperthreads per core would instead be:

siblings        : 4
cpu cores       : 16

Am I understanding this correctly? For that matter, is there a definitive publication about this? I've looked for it, and will continue, but no luck so far...

I think this signifies that hyperthreading is off (since siblings equals the number of cores). If hyperthreading were enabled I think it would say siblings=8.