A fibroblast is a type of cell that synthesizes the extracellular matrix and collagen,[1] the structural framework (stroma) for animal tissues, and plays a critical role in wound healing. Fibroblasts are the most common cells of connective tissue in animals.
For example, a 700 x 20 C road tire would be a 20-622; a 700 x 38 hybrid tire would be a 38-622. The width difference between these sizes would make them less-than ideal replacements for one another, but any rim that could fit one of them would work after a fashion with the other.
It tells us the size of the wheel that the tire is intended to fit. A size P215/65 R15 tire is made for a wheel with a 15 diameter. Load Index indicates the maximum load that the tire can support when properly inflated. You'll also find the maximum load on the tire sidewall, in both pounds and kilograms.