Broadly speaking, the word "ranking" is akin to the word "classification", whereas the word "rankings" deals with the positions of the given teams/players at the moment. Here is an example from a UK-based website:
The Official Red Dragon Darts World Ranking is issued every Monday following the completion of the previous weekend's qualifying tournaments. Every tournament from the PDC, WDF and BDO is included in the ranking, as well as many more.
On the same page you will find the word "rankings".
Darts Database - Red Dragon Darts World Ranking