Attenuation
Attenuation refers to the weakening of data signals as they travel through a respective media. Network media varies in its resistance to attenuation. Coaxial cable is generally more resistant than UTP, STP is slightly more resistant than UTP, and fiber-optic cable does not suffer from attenuation at all. That's not to say that a signal does not weaken as it travels over fiber-optic cable, but the correct term for this weakening is 'chromatic dispersion,' rather than attenuation.
It's important to understand attenuation or chromatic dispersion and the maximum distances specified for network media. Exceeding a media's distance without using repeaters can cause hard-to-troubleshoot network problems. Most attenuation or chromatic dispersion related difficulties on a network require using a network analyzer to detect them.