What is the differece between Usury and Trade?

Similarly, when usury and interest have been prohibited in the Holy Qur'an, they have become 

unlawful for all times, whether or not the Intellect is able to grasp the wisdom of this  injunction. 

While quoting the argument of the unbelievers, the Qur'an has said:

إِنَّمَا الْبَيْعُ مِثْلُ الرِّبَا

"Trade is just like Usury. 

Man earns profit from Trading (sale and purchase) and from usury also." 

Without explaining the difference between trade and usury, the Qur'an gave the following 

reply to the unbelievers:

D~scourseso n Islamic Way of Allah has allowed trading and prohibited Usury.

 (Ibid).

Now you have no business to object to this Divine Command, because when Allah has allowed 

trading, it is lawful;

and when He has forbidden usury, it is unlawful. To raise objections to this Divine Command is 

nothing but using the Intellect beyond its Jurisdiction.

source: Islahi Khutobat by Shykh Mufti Mohammad Taqi Usmani