a long narrow open container that holds water or food for animals:
a horse trough
a short period of low activity, low prices etc [≠ peak]
The graph showed peaks and troughs of activity.
the hollow area between two waves
a long area of fairly low pressure between two areas of high pressure
5 British English
if people have their noses in the trough, they are involved in something which they hope will get them a lot of money or political power - used to show disapproval