IPA: /ˌɪntərˈɪndɪˌvɪdʒuəl/
KK: /ˌɪntərˈɪndɪˌvɪdʒuəl/
Happening or existing between two or more people.
The study focused on interindividual differences in behavior.
Interindividual → It is formed from "inter-" (meaning between) and "individual" (from Latin "individuus", meaning indivisible or a single entity). The word refers to relationships or interactions that occur between individual entities.
Think of 'between' ('inter-') and 'single entity' ('individual') to remember that 'interindividual' describes something that happens between individuals.