Consciousness, at its simplest, is awareness of internal and external existence. However, its nature has led to millennia of analyses, explanations and debate by philosophers, theologians, and all of science. Opinions differ about what exactly needs to be studied or even considered consciousness. In some explanations, it is synonymous with the mind, and at other times, an aspect of mind. In the past, it was one's "inner life", the world of introspection, of private thought, imagination and volition. Today, it often includes any kind of cognition, experience, feeling or perception. It may be awareness, awareness of awareness, or self-awareness either continuously changing or not. The disparate range of research, notions and speculations raises a curiosity about whether the right questions are being asked.

चेतना (conciousness) कुछ जीवधारियों में स्वयं के और अपने आसपास के वातावरण के तत्वों का बोध होने, उन्हें समझने तथा उनकी बातों का मूल्यांकन करने की शक्ति का नाम है। विज्ञान के अनुसार चेतना वह अनुभूति है जो मस्तिष्क में पहुँचनेवाले अभिगामी आवेगों से उत्पन्न होती है। इन आवेगों का अर्थ तुरंत अथवा बाद में लगाया जाता है।