Wikipedia
(Spanish for galactics or superstars) are expensive, world-famous Real Madrid football players recruited during the "galácticos" policy pursued during Florentino Pérez's presidency at Real Madrid, where in his first tenure he purchased at least one galáctico in the summer of every year. Galácticos is now often used in a more general sense for a select list of football superstars in any team.
The term itself carries both positive and negative meanings. Initially, it was used to emphasise the greatness of signing superstar players and the construction of a world class team. Later the term attracted a more negative connotation; galáctico becoming synonymous with prima donna and used to deride the transfer policy and side (or team) built under it, following media perception that the policy at Real had failed to deliver expected levels of success.
The term has occasionally been used to describe other teams, both in football and in other sports, that have been perceived to follow a similar policy. For example, British rugby union commentator Martin Gillingham called French club Toulon "rugby's galácticos" in 2012 due to a wave of signings of international stars by owner Mourad Boudjellal.