I'm not a lawyer, but as per my understanding, you can use the EDN license, only for development & customization. You cannot use the software in production.
What this means is that one license allows one developer to develop customization and tools against the standard APIs. You cannot for example use the ArcGIS Desktop for Analyzing data or Creating maps. You cannot use the ArcGIS Server under this license for just publishing the service for commercial purposes.
The New site mentions:
EDN licenses are solely for the purposes of research, development, testing, and demonstration of your application. Each EDN subscription can only be used by a single authorized developer.
The older site is much more explicit:
- EDN software licenses are for the sole purposes of research and development only—internal development or development of government off-the-shelf (GOTS) or commercial off-the-shelf (COTS) products. EDN licenses may not be used for production or used by concurrent developers.
- EDN does not include the right to any deployments, run times, or server technology for production or commercial uses.
This information is valid in the US, but since you are in Turkey, you should confirm this information by talking to the ESRI distributor in your country.
Additionally, as Jens has mentioned in a comment below, EDN does not come with support. Support comes at an additional price of $2000 (at least in the US)