We conduct a systematic literature review on the concept of trust in the worldwide software ecosystem. We acknowledge that trust is something between two actors in the software ecosystem, and we examine what role trust plays in the relationships between end-users and (1) software products, (2) package managers, (3) software producing organizations, and (4) software engineers. Two major findings emerged from the systematic literature review. To begin, we provide a definition of trust in the software ecosystem, including a theoretical framework that decomposes and signifies a theoretical understanding of trust. Second, we provide a list of trust factors that can be used to assemble an overview of software trust.