Kotlin multiplatform is Kotlin's approach to the sharing of data models, logic, and domain expertise across multiple target platforms. The goal is to remove the need to write code multiple times for each of the various platforms you target. By leveraging shared expertise, shared code, and shared validation, developers can potentially reduce bugs, reduce the amount of code written, limit maintenance costs, and ship projects more quickly.
Because Kotlin can be compiled to many different build targets, developers can write code that can be deployed to these various targets while also still leveraging native components when needed.