We define scalar variable as IN, OUT, or INOUT and can be referenced anywhere in a procedure.
   lt_expensive_books = SELECT title, price, crcy FROM  :it_books  WHERE price > :minPrice AND crcy = :currency; 

In above assignment, the variable lt_expensive_books is bound.
Variable :it_books refers to an IN parameter of a Table type.
:minPrice and :currency refer to IN parameter of a scalar type.

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