The present preprint specifies and defines all Terms, Properties, Relationships and Axioms of ThingFO (Thing Foundational Ontology) v1.2, which is a slightly updated version of its predecessor, ThingFO v1.1. It is an ontology for particular and universal Things placed at the foundational level in the context of a four-layered ontological architecture named FCD-OntoArch (Foundational, Core, and Domain Ontological Architecture for Sciences). This is a five-layered ontological architecture, which considers Foundational, Core, Domain and Instance levels. In turn, the domain level is split down in two sub-levels, namely: Top-domain and Low-domain. Ontologies at the same level can be related to each other, except for the foundational level where only the ThingFO ontology is. In addition, ontologies' terms and relationships at lower levels can be semantically enriched by ontologies' terms and relationships from the higher levels. ThingFO and ontologies at the core level such as SituationCO, ProcessCO, ProjectCO, among others, are domain independent. ThingFO is made up of three main concepts, namely: Thing with the semantics of Particular, Thing Category with the semantics of Universal, and Assertion that represents human statements about different aspects of Particulars and Universals. Note that annotations of updates from the previous version (v1.1) to the current one (v1.2) can be found in Appendix A.