Although in popular parlance, sometimes people use "fad" to indicate a popular fashion they dislike and "trend" to refer to a fashion they like, in business the two are distinguished not by judgments of quality or taste but by statistical patterning. In other words, a fad shows a very steep increase in buying volume followed by an equally rapid drop-off, and a trend shows a somewhat more gradual curve. Both are characterized, like all fashions, by being ephemeral, rather than genuine needs or "classics" or "traditions" or "staples" or "habits" that persist over a long period.
Whether trend or fad, most of fashion relies on planned obsolescence, i.e. the notion that something is worn for a brief period and discarded with no regard to functionality. The entire concept of "fashion", therefore is one of the reasons for the huge ecological footprint of rich nations, and is based on a sort of class insecurity and conspicuous consumption detailed by Thorstein Veblen's seminal work, Theory of the Leisure Class.