A convex function is one where if you draw a secant line, the graph is below that. A quasiconvex function is a function where if you draw a (well larger of two) horizontal line the graph is below that. I know what those look like.
A horizontal line is above a secant line always. Pseudoconvex is between full and quasi.
What does pseudoconvex look like?
Here is an example, alongside other types of functions:
Pseudoconvex function is a function that behaves like a convex function with respect to finding its local minima, but need not actually be convex. Informally, a differentiable function is pseudoconvex if it is increasing in any direction where it has a positive directional derivative.