The general consensus is there's usually different partitions available:
- system
- data
- cache
- boot
- recovery
When a guide says to flash "partition" where partition is one of the above, then that implies transferring the contents destined for the partition. The mileage will vary depending on the handset/manufacturer as not all of them actually have implemented partitions like the above.
Usually it can be done with using the cable plugged in and using fastboot.
For example:
To flash a kernel onto the boot partition one can undertake it like this:
sudo fastboot flash boot boot_image_file.img
followed by:
sudo fastboot reboot
Likewise in the OP's case, its referring to the recovery partition.
sudo fastboot flash recovery recovery_image_file.img
I would be wary about using ROM Manager to do this for you without using a computer; Have got bitten by it, and found that it can sometimes, be incorrect with regards to using recovery i.e. ClockworkMod Recovery, it was so convinced that I had a very old version of CWM, when in reality, the latest was installed; end result, I messed up the recovery and threw away ROM Manager as I preferred to do it on the computer - less errors and that the human checking is in place.