Board Thread:New on Pretty Cure Wiki/@comment-25034020-20181022151836/@comment-1631127-20181027142511

CureHibiki wrote: ... have you never heard of the term "6th ranger"? It came from Power Rangers when Power Rangers always started with 5 heros and then mid way through, added a 6th Ranger. This has now become a term used by many Precure fans to imply that she is a mid season Cure... It also applies to Super Sentai or Power Ranger with groups of less than 4 members. Although it is recommended not to use it in that case.

In other words it refers to a member who enters the team during the middle of the series