DM provides implicit type conversion (coercion) between primitive types.

var/x = "string"
world << x // "string"
x = 5
world << x // 5

Say you have an /obj/honk object, you're fully able to assign it to a type-less var as we did before with our string and number; however, you won't be able to actually access any of the object's data without typecasting it first.

The syntax to cast a variable varname to the type your/type is as such:

var/your/type/varname = initialValue