There is no difference. If a person has obsessive thinking, then that person has OCD. Remember, you need to have only obsessions or compulsions for OCD, not both (though 96 percent of people with OCD have both). As long as the criteria for an obsession discussed before are met, then the diagnosis of OCD can be met. If, however, a person just can’t get a thought out of his or her head, and it is more of an annoyance than anything, this does not meet the criteria for an obsession. Almost all of us have experienced this at some time, but it does not mean that we all have OCD.
Something escalates to the realm of an obsession when it is intrusive and inappropriate, and a random thought typically does not reach that level. Further, people with OCD typically attempt to somehow neutralize an obsession, whereas individuals who experience a random thought just try to get rid of it and typically think nothing of it beyond it being a thought. Individuals with OCD give more credence to their thoughts than do people without OCD, believing that having had that thought makes them a bad person or that now that they have had that thought, it is likely to come true.