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Visually, a glaring person tends to have their eyes fixed and heavily focused on a subject. This can sometimes be considered synonymous to staring but, in most of the cases, staring is caused due to curiosity and lasts only for a short duration, whereas glaring is caused due to contempt and lasts for a relatively longer duration.
Many people glare at a subject to express disapproval of the physical nature of the subject or ideas that may be expressed by the subject.
See also 
|Look up glare in Wiktionary, the free dictionary.|