It is a concept introduced by Eric Evans that helps the technology work closely and align with the way the business works and represent the real world in code. It promotes collaboration of domain experts and software developers by using ubiquitous language within the bounded context of a domain across the business.
At the core of DDD is business domain which defines the problem that the business tries to solve. Business domain and its subdomains are defined during the strategic design. Once strategic design has been done, the next step is tactical design which essentially is a technical implementation. Both steps are important to be able to create a Domain Business Model.