The term 'Logical Prefix' refers to a word or phrase that is added to the beginning of another word to modify its meaning. In this case, the crossword solutions are SOCIO (5 letters), ASTRO (5 letters), and GEO (3 letters). SOCIO is derived from the Greek word for 'SOCIETY, ' and it is used to refer to the study of human SOCIETY and social relationships. ASTRO is derived from the Greek word for 'STAR, ' and it is used to refer to the study of astronomy and space. GEO is derived from the Greek word for 'EARTH, ' and it is used to refer to the study of geography and the physical features of the EARTH. All three of these prefixes are used to modify the meaning of other words in order to make them more logical and precise.