The difference between carbon credits, offsets and permits can be confusing. Fundamentally, carbon credits and offsets are the same thing, both being equal to one metric ton of GHG emissions. Some people argue differently, however. Most of the differences in their interpretation relate to the various scenarios (and carbon markets) in which they are used, and for what purpose they are used.
The simplest way to explain the differences is that a permit means that its holder has the right to pollute up to a certain level, whereas a carbon credit or offset is a certificate stating that someone else has made a commitment to reduce carbon emissions on behalf of the owner of the credit or offset.