Fluids given underneath the skin are called subcutaneous fluids. This therapy method is used in correcting and preventing dehydration and helping to flush waste products through your pet's system. This type of therapy is commonly used in diseases such as chronic kidney failure.
Fluid therapy may be done a couple times a week (depending on your veterinarian's recommendations) and will supplement regular water uptake. You will typically be provided with a vinyl bag containing fluid solution, a drip set line, and needles. It is important to follow instructions by your vet to keep the fluids sterile and keep these items from becoming contaminated.
The video shown demonstrates how fluids are properly administered.