Rascal is a high-level transformation language that aims to simplify software language engineering tasks like defining program syntax, analyzing and transforming programs, and performing code generation. The language provides several features including built-in collections (lists, sets, maps), algebraic data-types, powerful pattern matching operations with backtracking, and high-level traversals supporting multiple strategies. Interaction between different language features can be difficult to comprehend, since most features are semantically rich. The report provides a well-defined formal semantics for a large subset of Rascal, called Rascal Light, suitable for developing formal techniques, e.g., type systems and static analyses. Additionally, the report states and proofs a series of interesting properties of the semantics, including purity of backtracking, strong typing, partial progress and the existence of a terminating subset.