Even if in literature the role of environment in designing and engineering Multi-Agent Systems (MAS) has been largely acknowledged and explored, no abstract formal model have been developed so far to rigorously define the main features of environment programming in the context of MAS programming, in particular to be integrated and exploited with existing agent programming languages/platforms and related formalisations. Accordingly, in this paper we present a formalisation of a general-purpose model for environment programming, based on the notion of artifact as introduced in the A&A metamodel and implemented by the CArtAgO framework. Even if based on the A&A meta-model, we argue that the model can be useful to understand and analyse aspects that are important - more generally - for any general-purpose environment model used in MAS programming.