المعنى الاصطلاحي :

Keeping careful watch for possible danger, whether that danger is certain or not.

الشرح المختصر :

"Hadhar" (caution) is being cautious of what is yet to happen or what will probably happen. Islam called people to monotheism, warned them against polytheism, and ordered them to avoid whatever may lead to it. This could be achieved by being cautious of the danger of polytheism and its causes, like glorifying the dead, supplicating at the graves, building domes and mosques on graves, and so on. Islam also ordered the Muslims to be wary of imitating the polytheists in their feasts or in any of their characteristics. The target is to maintain and protect monotheism against whatever may weaken or eradicate it.

التعريف اللغوي المختصر :

"Hidhr" or "Hadhar": vigilance, watchfulness. Other meanings: readiness, preparedness.