If an app is optimized for iphone 5 will it still work for iphone 4?

I have an app, its free, and its for the iphone 5. I have iphone 4 and it works perfectly fine, besides being free and not everything is avaliable.

It'll still work perfectly. The only difference is that apps optimized for iPhone 5 have the app stretched a bit to fit the screen since it's bigger.

When they say it is optimized for the 5 they are referring to its 4" display. That's basically it.