Despite over a decade-long experience of implementing e-Participation initiatives, there have been limited efforts so far to develop a detailed, comprehensive conceptualization for e-Participation considered from three distinct perspectives: as democratic process, a project and a deliberation platform. Current e-Participation literature is replete with fragmented models, which only partially describe aspects of e-Participation with main focus on structuring the "e-Participation" concept as a domain. This has made consistent descriptions and comparative analysis of e-Participation initiatives difficult, thus hindering the overall evolution of e-Participation. Consequently, no comprehensive, formal, executable e-Participation Ontology exists, that could be directly leveraged to facilitate operations of e-Participation initiatives or improving communication and knowledge exchange between similar e-Participation initiatives. In addition, current generation of e-Participation models does not explicitly support the emerging phenomenon of spontaneous, citizen-lede-Participation, in particular hosted on the social media platforms. This work bridges this gap by providing a practical, yet sufficiently detailed, conceptualization along with corresponding formal and executable ontology for next generation e-Participation. These semantic models cover the core facets of e-Participation as a democratic process, an initiative and a sociotechnical system. The developed models also explicitly support the integrated citizen- and government-led model of e-Participation. For demonstration and validation, we employed the developed e-Participation Formal Ontology as a "design artefact" to describe two e-Participation initiatives at Local Government and European levels.