$FLEX$ 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
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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?