It looks like one of the widow spiders from the genus, Latrodectus.  But it is not a black widow spider.  This is a genus of spiders in the family Theridiidae, many of which are commonly known as widow spiders. The genus contains 32 recognized species distributed worldwide, including the North American black widows (L. mactans, L. hesperus, and L. variolus), the button spiders of Africa, and the Australian redback. Individual species vary widely in size, but in most cases the females are dark-colored and readily identifiable by reddish hourglass-shaped markings on the abdomen.

The venomous bite of these spiders is considered particularly dangerous because of the neurotoxin latrotoxin, which causes the condition latrodectism, both named for the genus. The female black widow has unusually large venom glands and her bite can be particularly harmful to humans. However, despite the genus' notoriety, Latrodectus bites are rarely fatal.