Analysis
Trend
Also called direction.
Trend is the underlying direction of a series after short-term noise is smoothed out. It is a read of the slope, not of any single day.
How it is measured
Estimate it by smoothing, with a moving average or a fitted line, over a window long enough to cover the cycle. Express it as a rate of change per period, such as plus 2.1 percent a week.
Check whether the trend holds across windows. A line that points up on a 4-week view and down on a 12-week view needs a longer look.
Worked example
A bakery's online order count goes 220, 235, 228, 241, 250, 244, 262 across seven weeks. A fitted line adds about 6 orders a week, about 2.6 percent.
Week 8 shows 235, a dip. Because the line explains the series, the baker does not change the menu on one weak week. Week 9 is 268 and the slope continues.
How it differs
A trend is the direction. A moving average is a tool to reveal it. The trend is what you want to know and the average is one of the ways to estimate it.
Common errors
Drawing a trend from three points. Ignoring seasonal shape. Extending a line far past the data. Reacting to one noisy week. Using different windows each time.
In practice
Look at the trend on at least two window lengths before reporting a direction. Mention the slope and the window. Treat a break in the line as an event to explain.