I frequent an online Rottweiler's Forum website. It's a community of Rottweiler owners, filled with posts categorized under different topics like Nutrition, Grooming, Behaviour and etc. There is also a category called the Rainbow Bridge. This is the explanation of what the Rainbow Bridge is.

*sniff

Just this side of Heaven is a place called Rainbow Bridge.

When an animal dies - one that has been especially close to someone - that pet goes to Rainbow Bridge. There are meadows and hills for our special friends so they can run and play together. There is plenty of food and water, sunshine and cozy beds, and our friends are warm and comfortable.

All the animals who had been ill and old are restored to health and vigor; those who were hurt or maimed are made whole and strong again, just as we remember them in our dreams of days and times gone by. The animals are happy and content, except for one small thing: they each miss someone very special, someone who had to be left behind.

They all run and play together, but the day comes when one suddenly stops and looks into the distance. His bright eyes are intent; his eager body quivers. Suddenly, he breaks from the group, flying over the green grass - his legs carrying him faster and faster.

You have been spotted, and when you and your special friend finally meet, you cling together in joyous reunion, never to be parted again. The happy kisses rain on your face; your hands again caress the beloved head, and you look once more into the trusting eyes of your pet - so long gone but never absent from your heart.

Then you cross the Rainbow Bridge together.

Author Unknown