Since trading with the trend is essential to exploiting the trend component of market price action, successful systems and approaches employ some method of identifying trend. A popular idea is a separate trend filter. This is an algorithm that preliminarily looks at recent price action and determines whether the trend is up, down or neutral. It is not essential that every approach have a separate trend filter. Some methods, such as moving averages, incorporate a trend indicator into the entry technique.
Many traders attempt to complicate the problem of trend identification.
They invent all kinds of fancy mathematical equations and methods of massaging past price action to more precisely determine whether the trend is up or down. I have long argued that this is pointless. Like all things in trading, simplicity is the best route. Of course, trend is only relevant in conjunction with a particular time frame. But once you identify the time frame, there is nothing fancy about the concept of trend.