After filing an application in one country (the “priority application”), an applicant then has the right to claim priority and file an identical application for the same trademark in another country for a period of six months.
If someone else attempts to file a conflicting trademark in that second country during that six-month period (the “intervening application”), some of the effects of the original applicant’s second application are effectively backdated to the date of their first filing. In the event of a dispute, this allows them to assert that the trademark is available and claim priority.