Both are the same. Flat fee discount stock uses these terms to tell the brokerage fee. The more accurate term among these is 'per executed order'.
Example:
5paisa, the discount stock broker charge flat Rs 10 per executed order brokerage fees.
If you place a limit order to buy 100 shares of Wipro, there are 3 possible scenarios:
You get all 100 shares
You get 80 shares only
You get 0 shares
In case 1 and 2; you pay flat Rs 10 brokerage. Irrespective of how many parts these trades took place, you pay one simple flat Rs 10 brokerage on this transaction at the end of the day.
You placed an order to buy 100 Wipro and 100 Infosys shares. These are considered 2 different orders and if executed successfully, you pay Rs 10 for each trade (total Rs 20 brokerage).