Conceptual Design is an early phase of the design process, in which the broad outlines of function and form of something are articulated. It includes the design of interactions, experiences, processes and strategies.
In an engineering product design environment, concept design or conceptual design is an early stage of a product design process. Within the new product development cycle, it typically sits between the product planning requirements and embodiment design.
On demand pull product developments the product requirement could be elaborate at the start and the concept generation phase falls within the product design process.
But on technology-push new product development, the front fuzzy end is rather confusion as at the start you have the technology (proven) but how that can be used to design products to sell is rather vague. Hence concept design falls at the start of with fuzzy end where you try out
Within the fuzzy end of new product development, concept and technology development plays a crucial role in identifying the products range and design etc. Within the product design phase concept design or conceptual design stage concentrates on the chosen design.