The basic idea of Quinian Boostrapping is that you start off not understanding a concept, but use a symbolic placeholder for it, and then fill in the details over time. For example, right now you don't understand Quinian Bootstrapping but you do have the placeholder term "Quinian Bootstrapping" that you can hold in your mind and relate to other things you know and learn. Over time, your placeholder is replaced with the actual concept.
Note that this is how nearly all of our concepts work. What is "water" or "planet" or "electricity"? You start off with "I learned some arbitrary word that picks out some category of thing in the universe" and then approach the real concept over time. But note that an "expert" on the concept may surprise you: "ice is a form of water even though you think it is not" and "Pluto is not a planet even though you think it is" and "the bright flashes during a storm and the stuff that makes the TV work are the same."
You asked specifically about weight. Imagine a child newly learning "weight" as opposed to "mass" (and as opposed to "density" and "volume" and other nearby terms). The child will start off just knowing that there are various terms that are picking out nearby concepts, but not understanding what makes them different. But as the child is led through examples (e.g., "the same object will weigh more on Earth than on Mars") the placeholders become elaborated into concepts.
This bootstrapping ability relies on being able to relate information from a variety of sources to an arbitrary placeholder symbol, which means it is likely unique to humans.