If a speaker considers that words do not have precise meanings, this concerns:

The answer is "ambiguity".

Ambiguity refers to the uncertainty of the meaning where an individual can draw multiple explanations from something. I give a simple example to make it clear, a sentence is "Tom reached the person with car", now in the given example it is unclear whether Tom had the car or the person he reached, this is ambiguity or as they call it having dual meaning.