The term parameter is in general used for both the definition of the argument that should be passed to an Entry, program, procedure, function or subroutine and for the argument that is passed. This poses a problem.
If I define a mathematical function f(x) = x + 2, the identifier 'x' is said to be 'the parameter' of the function f, meaning that it indicates the argument that should be passed. If I write down an application of the function f, e.g. f(3) 3 is also said to be 'the parameter' of the function f, meaning that it is the argument that is actually passed to the function f. When I talk about 'the parameter' of the function f it is not clear whether I mean x or 3.
In order to distinguish between these two uses of the word parameter we call an identifier that is used in the function definition to denote an argument that should be passed the Formal parameter (x in f(x) = x + 2). An expression that yields the argument that is passed is called an Actual parameter (3 in f(3) or a+b in f(a+b)).
A Formal Parameter is a Field that is needed to determine exactly which data set should be retrieved from the database. The definition of the formal parameters is stored in the Entry definition or function definition in the DID. Formal parameters have the same attributes as a field and in most instances, each formal parameter is also included as a Field of that Entry. It is then recommended that the formal parameters are defined exactly the same as the Field, including the name. The order in which the formal parameters are defined is significant.
Please note that the maximum number of formal parameters for an Entry is 23.