At its most basic - an equitime point (equal time point) is the point at which it will take you equal time to go to two different places. Its usually used when looking at diversion time.
So, if there is no wind, then the equitime point when you're flying from A to B is going to be half way between A and B. However if you've got a tailwind on that sector, then the equitime point is going to be closer to A (as to return there will have a slower groundspeed than going to B). It can also be between off track locations - but its just a general example.
15 Years has been entered into the scratchpad - where you type something before selecting it into a position. It might be worth noting that Air Tahiti Nui started operations 15 years ago...