$FLEX$ and $PROFILES$ in Oracle Apps

What is $FLEX$ and $PROFILES$?

$FLEX$ and $PROFILES$ are Special Variables in oracle Apps environment and are used to hold values at runtime.
Every Oracle Apps technical consultant will be familiar with the term $FLEX$ and $PROFILES$. Whenever we are working with value sets, we will be using both of these for modifying the data fetched, for basing the values of a parameter on the other parameter and also fetching the Profile Option values.
To segregate this based on the functionality
$FLEX$: Used for basing the value of a parameter on another parameter.
$PROFILES$: used for fetching the data stored in the specified profile option value which is currently active.

Where is it used? 

Both these variables are used in the Parameter form of a Concurrent Program and are used at the Where Clause window in the value set of Table type.

Syntax: 

:$FLEX$.previous_value_set_name
Important:

• $FLEX$ must always be in capitals.
• A ‘:’ must precede the declaration of $FLEX$.
• The previous value set name must have already been assigned and saved on a different parameter.

:$PROFILES$.Profile_option_name 

Important: 

• $PROFILES$ must be always in capitals.
• ‘:’ must always precede the declaration.
• Profile option name is the Profile Name and not to be confused with the User profile Name.