It refers to all payments to employees which were not paid regularly at each pay period, including bonuses paid at fixed periods, but not paid regularly at each pay period and bonuses linked to individual or collective performance. These bonuses are not included in the hourly and monthly earnings. In some tables presenting monthly earnings, an estimation of the monthly value of the bonuses is included separately. Bonuses are included in annual earnings.
Community statistics on the level and structure of labour costs 1996 - List, definition and breakdown of the variables, p.5
Eurostat, "Statistics on the structure and distribution of earnings: Methods and definitions", Data 1995, 1998 Edition, Office for Official Publications of the European Communities, Luxembourg, 1999