Job Profile (sometimes also referred to as a 'user profile') refers to the main function or level a person has in an organization. Some examples are junior developer, senior salesperson, manager. You have the flexibility to define the profiles that are relevant to your organization. ClayHR comes with predefined profiles that you can keep, edit or remove.
Job titles are specific titles given to individual employees, and can vary more freely compared to job profiles. Generally, an organization will have a finite set of job profiles, and a larger, more fluid set of job titles.
Project roles (sometimes also referred to as user roles) are used in the context of projects. Regardless of what profile a user has (developer, salesperson, etc), they can play different roles in a specific project. Some examples are Team Lead, Reviewer, Quality Assurance. A user can be part of different projects, and play different roles in those projects.
For instance, Martha is an 'Astrophysicist', which is her job profile and plays the role of 'Team Lead' which is her user role for the project titled "Land Person on Mars 2030". However, she plays the role of 'Reviewer' in another project called "Asteroid Kinetic Energy Harvester".
User Group is used in ClayHR in the context of security, to define user access levels and permissions in the application. User groups determine who can access what and what level (view only, edit, manage, delete, etc).