Opportunistic network (oppnets) is a promising paradigm, which allows communication to be set up between nodes even without infrastructure in a delay tolerant fashion. It has even become more pertinent with the proliferation of varieties of autonomous mobile devices. However, malicious devices pose potential security threats (packet dropping, eavesdropping, Denial of Service (DoS) attack, black hole attack, Identification (ID) spoofing, etc.) to the performance of oppnets, due to the inherent characteristics of such networks like ever changing network topology and lack of a definite communication path between nodes amongst others. Recent focus on mitigation mechanisms for security threats in oppnets is on trust management since various mechanisms have been used, but the trust-based methods appeared to meet up with the security requirement of the opportunistic network better. However, no work strictly present trust management extensively. This paper presents trust management together with trust related issues in oppnet (trust-based security threats, trust mechanism, and the trust management scheme as oppnet security solution). It is aimed at providing the reader a clear understanding of trust management (preferred solution) within a single literature.