Fads and Trends:

A trend is a line of general direction of movement, a prevailing tendency of inclination, a style or preference, a line of development, or the general movement over time of a statistically detectable change. In a few words, "trend" is a synonym to "tendency". The biggest example of trend is the long shirts that are in fashion nowadays or has become a trend.
A fad is a temporary period of unusually high sales driven by consumer enthusiasm and immediate product and brand strategy or a practice or interest followed for a time with exaggerated zeal. The nature of fad is individual. It could be called as an individual society's over interest in some thing which is considered to have consist of some virtue i.e fad diet, exercise etc. Its example can be the opening of Hardees in Pakistan. It is gaining huge popularity in Pakistan irrespective of the fact that it's expensive.