Many advanced countries are recognizing more and more the importance of teaching computing, in some cases even as early as in primary school. "Computational thinking" is the term often used to denote the conceptual core of computer science or "the way a computer scientist thinks", as Wing put it. Such term - given also the lack of a widely accepted definition - has become a "buzzword" meaning different things to different people. We investigated the Italian primary school teachers' conceptions about computational thinking by analyzing the results of a survey (N=972) conducted in the context of "Programma il Futuro" project. Teachers have been asked to provide a definition of computational thinking and to answer three additional related closed-ended questions. The analysis shows that, while almost half of teachers (43.4%) have included in their definitions some fundamental elements of computational thinking, very few (10.8%) have been able to provide an acceptably complete definition. On a more positive note, the majority is aware that computational thinking is not characterized by coding or by the use of information technology.