Profiles are IzoT resources similar to a data type definition for a block. Every block is based on one profile, but your application may implement multiple blocks based on the same profile, or based on different profiles.
For example, the environment sensor example application included with the IzoT Device Stack provides a temperature sensor block, a humidity sensor block, and a motion detection sensor block, and each one is based on a corresponding profile resource, as well as associated hardware (motion detector, temperature sensor, etcetera).
Definitions of profiles are available in the embedded python documentation in the izot.resources.profiles package.