What does it mean if a rash has raised boarders?

Nonspecific. Many rashes have raised borders. The most common is probably ringworm, but there are numerous others, including psoriasis, eczema, certain skin infections, and a host of other (rarer) diseases. It is not usually a danger sign, if that's what you're asking. The only way to know for sure is to let a dermatologist examine it directly.