Mae Carol Jemison

Designers conceptualize. They create a concept based on education, experience and best practices. These are called plans, blueprints or designs.

Engineers actualize. They take concepts and implement them. This involving actually building and rendering them in physical reality.

In simple words, we can say that a designer sees the product from outside whereas engineer sees the product from inside. There is a thin layer between designer & engineer which is very hard to differentiate that in most of the time all engineers are designers but not all designers are engineers. Design does not have a limit as is the work of your creativity. The engineer is personally responsible for safety of the system. In many fields it is possible for the engineer to be completely unrelated to the design process & only be responsible for the validation of the design.

In some engineering disciplines; the concepts of “design” and “engineering” are segregated (“implementation” may be further segregated, but that particular topic has already been done to death in the area of programming). It is occasionally argued that such separation is beneficial to software systems, as well.

In general (feel free to ReFactor this definition):

Design consists of the specification of requirements (functional, etc.) needed to satisfy the customer and other relevant external parties (the law, etc.) The job of a designer is to gather such requirements from various sources – asking customers directly, market research, academic research into relevant fields, DomainKnowledge, study of the law and of relevant standards and practices, and a bit of intuition/foresight, and produce a specification of some sort (the exact form is probably not important for this discussion). The designer is concerned with many HumanFactors – aesthetics, functionality, ease-of-use, fitness for purpose, and quality; the designer is less concerned with implementation details.

Engineering consists of the translation of these requirements into a technical specification describing a system which conforms to these requirements (which could be then implemented by persons knowledgeable in the craft). Again, the exact form of the technical specification is not important here. In many traditional engineering disciplines, the role of engineer is generally not concerned with things such as aesthetics or fitness-for-purpose; instead the engineer is concerned with coming up with a system (or specification) which is correct, safe, and cost-effective. The chief distinction between an engineer and a designer is that the engineer is personally (legally speaking) responsible for knowing said correctness and safety of the system. The processes of technical specification and other standard procedures exist so that the engineer can convince himself and others of this knowledge. In many fields it is possible for the engineer to be completely unrelated to the design process and only be responsible for the validation of the design.

The very short answer:

Design is what to make.

Engineering is how to make it.

Technology is the product.