Double apex
A double apex is a long corner taken with two separate clipping points, often with a slight drift out to the middle between them.
Also called: two-apex corner
Some corners are too long, or shaped too irregularly, to be taken as one arc. They might be two corners joined together, or a long hairpin with a kink. In these, the fastest line usually touches the inside twice: once early in the corner, then again later, with the car drifting a little toward the middle between the two.
Think of it as two corners where the first exit is a compromise for the second entry. You often brake for the first apex, maintain or barely add speed through the middle, and then focus on the second apex because it leads onto a straight. The second clip is usually the more important one.
Drivers new to a double apex often try to hug the inside the whole way, which makes the corner tighter and slower, or take a single wide arc that blows the second apex. Ask an instructor which part of the corner pays off, then pick reference points for both clipping points.
Treating a long corner as two linked apexes usually raises speed through the middle and protects the exit that matters.
Simplified 90° corner. Real corners trade entry, mid-corner and exit speed differently; what follows the corner decides which matters most.