A leader's job is to lead a team, by improving relationships, handling HR and project related tasks.

They are differentiated from lead designers, who are not leaders, but designers that lead the overall construction of a project, but not the entire team.

A design can refer to 2 things:

• The design of product, i.e. what it should do, how it should be constructed, etc. Usually comes in the form of a design document
• Hardware design, which is the final physical look of a piece of hardware

Unless hardware is specifically used, design will refer to the first of these 2, e.g. a description of how a product should work and be constructed.

Projects refer to a product that is being created, but is not yet finished.

This is the final output of a company. It can either be a hardware or software product. Before the product is finished, it is referred to as a project still, as it may never come to fruition.

Development refers to the entire process of creating a product, from the design phase to the alpha phase and finally the beta phase.