I am applying for a Ph.D. position at Netherlands and I see that there will be a promoter and an advisor. I have never seen such a title as "promoter". What is the difference between the two titles?
As far as I understand, in the Netherlands, only full professors may be appointed "promoter", i.e. the official advisor, the super-boss if you will. Other faculty members must apparently get authorization from the university (see comment).
So if you are going to be supervised by someone who is not full professor (e.g. associate/assistant professor), that person will be appointed as "(co)advisor", while a full professor will be acting as an official advisor/promoter and will chair the doctoral examination committee.
To add to the previous answer: an advisor is likely to be your daily supervisor, meaning that you have most contact with him/her. This person can also be a full professor. Your Promotor is a full professor (often head of department) who is likely to be too busy to meet often (though their level of commitment differs). An assistant professor is (since a couple of years) allowed to also be a promotor.
In short: the advisor is someone you'll spend more time with and should be there to help you with practical matters.