For the purposes of this Directive the following definitions apply:

(a) "supplementary pension" means a retirement pension provided for by the rules of a supplementary pension scheme established in accordance with national law and practice;

(b) "supplementary pension scheme" means any occupational retirement pension scheme established in accordance with national law and practice and linked to an employment relationship, intended to provide a supplementary pension for employed persons;

(c) "active scheme members" means workers whose current employment relationship entitles them or is likely to entitle them, after fulfilling any acquisition conditions, to a supplementary pension in accordance with the provisions of a supplementary pension scheme;

(d) "waiting period" means the period of employment, required under national law or by the rules of a supplementary pension scheme or by the employer, before a worker becomes eligible for membership of a scheme;