I assume you don't mean 'learned' in any sense related to cognition/conciousness/intelligence
Here's a pretty good starting point for (what should be) a discussion (on the Sound Science forum) regarding materials with memory:
'...
materials with memory, also referred as
materials with hereditary effects are a class of materials whose
constitutive equations contains a dependence upon the past history of
thermodynamic,
kinetic,
electromagnetic or other kind of
state variables.'
Essentially, it means that something done to the material in the past affects its future performance. A simple example we can all relate to is when you flex something (say a plastic rod) enough (times or amount), it will change the object, weakening it, making it more flexible, changing the color of the object...eventually resulting in changed behavior (say not rebounding as quickly, or not returning to its initial shape).
Another good/familiar example is battery memory.