Sounds like you may be talking about optional parameters...

DECLARE

@BusinessEntityID INT = NULL,

@FirstName VARCHAR(50) = 'John',

@LastName VARCHAR(50) = NULL;

SELECT

p.BusinessEntityID,

p.PersonType,

p.NameStyle,

p.Title,

p.FirstName,

p.MiddleName,

p.LastName

FROM

Person.Person p

WHERE

(p.BusinessEntityID = @BusinessEntityID OR @BusinessEntityID IS NULL)

AND (p.FirstName = @FirstName OR @FirstName IS NULL)

AND (p.LastName = @LastName OR @LastName IS NULL)

OPTION(RECOMPILE)

;