This paper presents a top-level ontology framework for Human-Centered Digital Twins designed to enhance semantic interoperability and reasoning in socio-technical systems. Existing ontologies are typically domain-specific, which eases coverage of a specific domain but limits cross-domain reuse and adaptability. Addressing this gap, the proposed ontology is structured around three foundational concepts: Digital Twins, Human-Centricity, and Socio-technical System Actors within the system. The ontology was developed following established ontology engineering practices, with emphasis on modularity, reusability, and formal representation of key concepts. It supports the integration of sensor observations, interaction modalities, and representation of human-centricity factors. Its applicability is demonstrated through a logistics use case, which involves cognitive decision support for yard operators and forklift drivers engaged in short-term scheduling of yard operations. The ontology offers a reusable semantic foundation that supports integration, context representation, and human-centric system modelling and can be extended to diverse domains.