SVG is a vector graphics format backed up by W3C. It’s all XML and is quite a nice technology. At the moment native browser support is pretty much non-existant (Mozilla has a special build with SVG support). Adobe has a decent SVG plugin, but it’s still a plugin. I think it’ll take years to get native SVG support for browsers.
Some people consider SVG and Macromedia’s Flash format to be competitors. To me they’re not really competitors since Flash has superior scripting and animation features. SVG has a few other advantages; It’s clean, indexable XML and you can use a normal CSS file to determine fonts, colors and such.
I wish Macromedia would jump on the SVG bandwagon. This way SVG could be used for graphs, etc. and Flash for more complex things. I don’t know how people at Macromedia see it, but I’d really like to see SVG support in the next version of it’s widespread plugin.