A good question.
It has no specific name. And that is probably the reason that far too many graphs are incorrectly published without it. Call it squiggly line, squiggily line, lightning flash. But make sure you use it when appropriate. Meanwhile, I will investigate further.
The steepness of a line graph is called the "gradient" ------------------------------- or slope.
line graph
the graph is called a line
a line graph
nonlinear line
nonlinear graph.
nonlinear graph
"Slope" is the steepness of the line on any graph.
It is called, not surprisingly, a combination graph.
A continuous graph ?
The line that reflects the general pattern of a graph is called a trend line.
It is formally called the slope of the line.