Academic name for graphs which curve like a bridge

Solution 1:

This being sales data and not a pure function, I wouldn't advise using an academic description. I'd expect sales data at a micro-level to move in a geometric manner, due to the nature of communication. The example graphs look polynomial.

If I were instructing someone to draw this graph, I would tell them to draw a parabola whose endpoints approach positive/negative infinity.

Referring to the "low point," I'd call it this valley's local minimum. Unless it was the lowest point in the range, which would be the absolute minimum.

Solution 2:

Positive convexity means concave up. Negative convexity means concave down. The positive and negative refer to the positive/negative value of the rate of change of the function f'. (To understand the meaning rate of change you need to at least do Calculus 1)

It is a commonly used term in finance.

See definitions below:

Investopedia: Convexity

Corporate Finance Institute: Negative Convexity.