To do that, they need to be able to describe as simply as possible the important concepts they want to use, and to find words that represent them as unambiguously as possible. That sounds simple, but it's actually not easy to do. For example, many people make no clear distinction between a term and a concept. To put the point rather starkly, terms have meanings but concepts do not. A concept is the meaning of a term, and cannot have another meaning.
Terms are the short-hand words or phrases used to point to such a concept.
However, concepts are important or not depending on their use in propositions or theories. Theories are statements involving concepts that are related to each other. Thus a theory is a package linking concepts each of which is represented by one or more terms. To illustrate this point, consider that to identify any concept we need a statement that establishes its necessary characteristics. Variables that may or many not be included in a concept can, however, be linked to it by theoretical propositions.