As I mentioned elsewhere, you can define a full cycle of a waveform as consisting of 360 degrees, akin to a circle. One quarter of the way around this circle – or moving to a point that is one quarter of the way through a cyclical wave – is 90°. A sine and cosine wave are shifted 90° degrees or a quarter cycle out of alignment (phase) with each other. Since this is a quarter of a cycle, this is often referred to as a quadrature relationship.
It turns out that having a pair of low frequency oscillators 90° out of phase creates some interesting effects. For example, when you have two LFOs driving a pair of panning circuits creates an interesting “chasing” effect; when they are two quadrants (180°) out of phase, you get a ping-pong effect. Therefore, some oscillators have quadrature outputs that are multiples of 90° out of phase with each other. (There are also highly specialized applications such as frequency shifting where quadrature oscillators come in handy.)
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