A linear trend is one that is best approximated by a straight line. Sometimes we use a straight-line approximation, even when it may not be a very good fit, because we are only interested in the sign of the slope, or its approximate magnitude. The parameters of a linear trend are about the easiest to calculate (though it doesn't matter much if an appropriate tool is used).
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<u>Non-linear trend</u>
A non-linear trend is one that is best approximated by a curve other than a straight line. Trig functions (sine, cosine), exponential functions, quadratic functions are often used. Non-linear trends are not restricted to these kinds of functions.
