When you hear there's a risk for severe storms do you ears perk up a little more than when you hear there's a chance for a pop-up thunderstorm? If not, they should.
There is a difference between a severe thunderstorm and your typical afternoon pop-up thunderstorm we see a lot during the summer. This is not to say you shouldn't respect the power of storms not deemed "severe" because all storms are powerful and can be dangerous.
However, severe storms are of particular concern and can pose significant life-threatening conditions. This is why the National Weather Service sends out warnings when a storm is reaching severe criteria. A severe thunderstorm warning is issued for storms that reach certain criteria.
The NWS official specifications for a severe thunderstorm include:
A storm capable of producing hail an inch in size or larger. That's about the size of a quarter. Hail this size can do damage to property easily.
A storm with wind gusts over 58mph. Wind gusts this strong can break tree branches.
Severe thunderstorms are also more likely to produce tornadoes, excessive lightning and flash flooding.