Applicants who pass a competition for permanent officials are placed on a reserve list from which the institutions draw recruits as and when they need them. The aim of a competition, then, is not to fill a specific post, but to constitute a reserve pool for recruitment needs as they arise.
If you are one of the highest-scoring applicants in the assessment phase, you will be placed on the reserve list. This means you may be selected for a job interview at one of the EU institutions.
Reserve lists for generalist competitions are valid for 1 year. For other profiles, they are valid for longer.