The trend means the direction in which the forex market is going up or down. So long as taking a look at the random-walking market movement on the chart, there clearly exist some tops and bottoms and the direction of those positioning decides the trend. The up trend is in the rising condition which makes the new top higher than the previous. On the contrary, the down trend is declining condition which makes the new bottom lower than the previous one. Once a certain trend is developed, this tendency is much sustainable. Stronger the power, the effect would continues so longer, from the short term to the middle term, and from the middle term to the long term. Those are simply regulated by a trend line, which has another face not to change so much.
The trend follow indicates positioning in line with the current trend, in which players would always take long position in case of up trend and would take short position in case of down trend. If you don't intend to trade for short term, you had better follow the trend which controls the forex market whole day.