A conservative GC will look for memory addresses on the stack/heap and assume they're all references to objects. This means that if you have an pointer-like val

A conservative GC will look for memory addresses on the stack/heap and assume they're all references to objects. This means that if you have an pointer-like value (e.g. an integer in the same range as where your objects are stored), the garbage collector will (falsely) think you're referencing this object and it will be not collected. A precise GC knows exactly what data on the stack/heap are object references and only scans these.