Could be hop oil.
Secondaries are generally not advised, unless racking onto fruit or other additions, or conditioning for months like a Russian Imperial Stout, in which case glass carboy filled to the neck so top surface is minimized for oxygen.
The oiliness is really not apparent in your photo. Can't tell what it is from this.
How much head space do you have in your secondary vessel? There should almost none (if a carboy/gallon jug, fill it right up into the neck). There's really not a lot of activity in this vessel, and there needs to be very little headspace. Oxygen in headspace can promote bacterial/fungal growth (which may or may not be the case, here). Top off with more cider or apple juice.
I wouldn’t worry. When I’ve had a pellicle (caused by wild bugs) it’s always been with fresh pressed juice and it usually doesn’t show up until a month or so after fermentation was complete.
See if it’s something your yeast is gonna clean up.
Thanks every ones. Here are some better pictures.
It seems like the head space might be a problems that I should deal with. Considering that I have three carboys, would it be a good idea to top up two of it with the third one and then to bottle what’s left out of the third? Maybe the cross contamination is to be considered as well?!..