Inward light
The Inner Light, or "the Light within" is a concept central to Quaker philosophy. It refers to the Quaker belief that God speaks directly to everyone, and that in order to hear it one must learn to be a good listener (generally through silent meditation), and give God a chance to speak through you.
It is important to note that this divine guidance (or "promptings or leadings of the Spirit") is considered to be distinct both from impulses originating from oneself and general moral guidelines. Quakers are inherently suspicious of hard and fast rules, as evidenced by the postscript that a Quaker meeting attached to a list of "Advices" published in 1656:
Dearly beloved Friends, these things we do not lay upon you as a rule or form to walk by, but that all, with the measure of light which is pure and holy, may be guided: and so in the light walking and abiding, these may be fulfilled in the Spirit, not from the letter, for the letter killeth, but the Spirit giveth life.[1]
To paraphrase, human laws are fallible, and ultimately we must rely on that of God within us in order to conduct our way through the grey areas of life; right action cannot be legislated. This does not mean that individuals must make their own decisions in isolation, however: Quakers often gather together to address sticky questions in a clearness committee or meeting for discernment.
Compare and contrast the Inner Light with the similar concept of an Inward Light, which appears in older Quaker writings but seems to have fallen out of use. This evokes an image of people reflecting the light of God rather than having a light source inside them.