Semantic annotation is one of the useful solutions to enrich target's (systems, models, meta-models, etc.) information. There are some papers which use semantic enrichment for different purposes (integration, composition, sharing and reuse, etc.) in several domains, but none of them provides a complete process of how to use semantic annotations. This paper identifies three main components of semantic annotation, proposes for it a formal definition and presents a survey of current semantic annotation methods. At the end, we present a simple case study to explain how our semantic annotation proposition can be applied.The survey presented in this paper will be the basis of our future research on models, semantics and architecture for enterprises systems interoperability during the product lifecycle.