This is the 7553rd most frequent Japanese word.
凸
"凸" means "convex" or "protruding" in English.
In this sentence, '凸凹' ('bumpy') uses '凸' (protrude) combined with '凹' (recess) to describe an irregular surface.
この道路は凸凹していて運転が難しいです。
This road is bumpy, making driving difficult.
Here, '凸' ('convex') refers to the outward-curved shape of the lens.
凸レンズは光を収束させます。
Convex lenses converge light.
In this usage, '凸っている' ('protrude') metaphorically describes standing out or being prominent in nature.