armhf stands for "arm hard float", and is the name given to a debian port for arm processors (armv7+) that have hardware floating point support.
On the beaglebone black, for example:
:~$ dpkg --print-architecture
armhf
Although other commands (such as uname -a or arch) will just show armv7l
:~$ cat /proc/cpuinfo
processor : 0
model name : ARMv7 Processor rev 2 (v7l)
BogoMIPS : 995.32
Features : half thumb fastmult vfp edsp thumbee neon vfpv3 tls
...
The vfpv3 listed under Features is what refers to the floating point support.
Incidentally, armhf, if your processor supports it, basically supersedes Raspbian, which if I understand correctly was mainly a rebuild of armhf with work arounds to deal with the lack of floating point support on the original raspberry pi's. Nowdays, of course, there's a whole ecosystem build up around Raspbian, so they're probably not going to abandon it. However, this is partly why the beaglebone runs straight debian, and that's ok even if you're used to Raspbian, unless you want some of the special included non-free software such as Mathematica.