The track flare of a bowling ball is the oil rings around the ball. Because of the forces at work within the ball, most balls today do not roll over the same line twice, creating a new line for each revolution of the ball. There are two points on the ball at which these lines cross and the one closest to the fingers is referred to as the Bowtie. When a ball flares, the Axis Point shifts in a straight line towards the Mass Bias of the ball.
Track flare can be manipulated using the Pin location and an Extra hole, and certain balls with aggressive cores and coverstocks can be drilled to overflare. Overflare occurs when the Positive Axis Point AND the bowtie actually shift as the ball is rolling down the lane. If you chart the movement of the PAP on a ball that is overflaring, it shifts in a curved line that looks like a "J".
For differences between Symmetric and Asummetric track flare see Track Flare Chart