It refers to the wind speed of the storm.
Hurricane Isabel was a category 5 hurricane.
Hurricane Michael was a Category 5 hurricane. It made landfall in the Florida Panhandle on October 10, 2018, with maximum sustained winds of 160 mph. It was the first Category 5 hurricane to make landfall in the United States since Hurricane Andrew in 1992.
The first category of a hurricane is category 1.
Hurricane Andrew was a Category 5 hurricane with 175 mph winds. The pressure was 922 mbar.
Category two
It was a category 1 hurricane.
Hurricane Tanya was a category 1.
Hurricane Arthur (2014) was a category 2 hurricane.
Hurricane Chris of 2012 was a category 1 hurricane.
Hurricane Ike is a category 4 hurricane.
The "stage" of the hurricane is it's intensity in size and wind speed. Category One is just a nasty tropical storm with an attitude. Category Five is a horrifically devastating monster hurricane.
Dennis was a category 4 hurricane.