To put it in more correct technical terms than TRiG:

 > 6: Then, if the element is one of the void elements, or if the element is a foreign element, then there may be a single U+002F SOLIDUS character (/). This character has no effect on void elements, but on foreign elements it marks the start tag as self-closing.

(Source: http://dev.w3.org/html5/spec-author-view/syntax.html#syntax-start-tag)

And foreign elements are:

 > Elements from the MathML namespace and the SVG namespace.

(Source: http://www.w3.org/html/wg/drafts/html/master/single-page.html#foreign-elements)

Thus at the very least we can conclude the character has no effect whatsoever, and it also does not close the tag or anything along those lines. So in the wise words of the great Quentin:

 > The slash is just syntactic sugar for people who are addicted to XML.

(Source: https://stackoverflow.com/a/3558200/1266242)