Only in JavaScript, variables can have an unspecified type. This only occurs if you don't assign a value or specify a type while declaring the variable.

JavaScript: The type specification is not necessary.

var playerLife : int;  // statically typed (because type specified)
var playerLife = 2;  // statically typed (because type is inferred from valueassigned)
var playerLife;  // dynamically typed (because neither a type or value is specified)

The dynamically typed variables will cause slower performance, and you can run into casting problems. You can use #pragma strict, including it at the top of a script, to tell Unity to disable the dynamic typing in the script and report compile errors when this is a dynamic type in the script.