1. to develop, to make accessible (For natural resources, land that you make ready for building. Also for markets in an economic sense.)
2. to make accessible (For knowledge, often used with a self reference in Dative "sich etwas erschließen". )
3. to become understandable ("sich jemandem erschließen" - for information and logic that "opens itself" up to someone. Essentially, a twisted alternative for "understanding".)
