I am reading the book "Multiple input describng functions and nonlinear system design" written by A.Gelb and W.E.Vander Velde.

At some point it says:

Single-valued characteristics are termed memoryless; multivalued characteristics are said to possess memory.

I am a bit confused about the meaning of the 'memoryless' term. I thought that memoryless meant a function that depends only on the value at that time instant and not at previous instants of time.

What am I missing?

$$y(t) = F(x(t))$$
where $y=F(x)$ is an injective function (i.e. each $x$ is mapped to only one value $y$).