To "operationalize" a concept is to turn it into something that can be measured. This is fairly simple, but examples of how concepts are operationalized shows just how important, and complicated, it can be to operationalize a theory.
For example, suppose that a sociologist has the theory that education and wealth are related in a community. This is a fairly basic theory, but how to measure it? The sociologist could possible define the three parameters as:
- Percentage of people with High School Diplomas
- Percentage of people who have gone to college
- Percentage of people who have completed college
- Average years of schooling
- Mean income per capita
- Median income per capita
- Mean household income
- Median household income
- Net worth per capita
- Net worth per household
- Poverty rate
This is of course an example, and even within this example, there could be even more possible definitions given for each one of the concepts. This makes finding the best way to model the concepts very hard for the good researcher. It also makes finding a way to skew and distort data easy for the biased researcher: The above combinations would give over 100 different possible answers to the question of whether there was a relationship, and what type of relationship, between the concepts. Some of these may give answers that do not truly reflect the situation.
This is why it is important to operationalize your concepts into measurable variables, and also to be wary when reading other's research.