Wikia

Spirit Bond
Spirit Bond (Passive) Passive While your pet is active, you and your pet will regenerate 2% of total health every 2 sec.
Usable by
Class	Hunter
Properties
School	Nature
Talents
Talented	Yes
Level required	45
Related buff
Spirit Bond Regenerate 2% of total health every 2 sec.
TCG image

“

After the hunt, we rest here as one entity and together feel our strength return.

”

Spirit Bond is a hunter talent available at level 45.

Notes

This helps you and your pet stay alive but it doesn't stop you or your pet from getting killed.
At higher levels with more Stamina, it begins to count almost as much as a free tic of Mend Pet.
It seems to generate some threat on your pet. (You shouldn't have taken any damage for the tic to affect you, thus removing the possibility of gaining any aggro from this buff.)
The range is self & pet. There is a point where it breaks off but it's not specified in game.
Generally only breaks when you and your pet are separated to the point of the pet despawning or your pet being killed.

Patch 5.0.4 (28 August 2012): Updated.
/ Patch 3.0.2 (14-Oct-2008): Also increases healing done to you and your pet by 5/10%.
/ Patch 2.0.1 (05-Dec-2006): Fixed an issue that was putting Hunters back into combat when they have the "Spirit Bond" Talent or have the Cryptstalker set bonus.