Attention or focus, is the concentration of awareness on some phenomenon to the exclusion of other stimuli. It is the selective concentration on discrete information, either subjectively or objectively. William James (1890) wrote that "Attention is the taking possession by the mind, in clear and vivid form, of one out of what seem several simultaneously possible objects or trains of thought. Focalization, concentration, of consciousness are of its essence." Attention has also been described as the allocation of limited cognitive processing resources. Attention is manifested by an attentional bottleneck, in terms of the amount of data the brain can process each second; for example, in human vision, less than 1% of the visual input data stream of 1MByte/sec can enter the bottleneck, leading to inattentional blindness.

ध्यान या अवधान (attention) चेतन मन की एक प्रक्रिया है, जिसमें व्यक्ति अपनी चेतना बाह्य जगत् के किसी चुने हुए दायरे अथवा स्थलविशेष पर केंद्रित करता है। यह अंग्रेजी "अटेंशन" के पर्याय रूप में प्रचलित है। हिंदी में इसके साथ "देना", "हटाना", "रखना" आदि सकर्मक क्रियाओं का प्रयोग, इसमें व्यक्तिगत प्रयत्न की अनिवार्यता सिद्ध करता है। ध्यान द्वारा हम चुने हुए विषय की स्पष्टता एवं तद्रूपता सहित मानसिक धरातल पर लाते हैं।