The term 'heart or centre' can be summarized by the crossword solution 'CORE', which is a 4-letter word. The term 'heart or centre' is often used to refer to the most important part of something, such as the CORE of an apple or the CORE of a person's beliefs. It can also refer to the center of a group or organization, such as the CORE of a family or the CORE of a business. In general, the term 'heart or centre' is used to describe the most important and influential part of something.