In starship classification, a heavy warship was a type of warship that was more heavily armed and armored then a standard warship.
The Romulan heavy and strike warbirds were the equivalent of heavy warships. (Ship Recognition Manual, Volume 5: Starships of the Romulan Star Empire)
In the beginning of the 29th century however, a new class of Warship was designed and built by the United Federation Starfleet, or commonly called the UFS.
The organization of the Federation called the United Federation Starfleet, or simply the UFS—was a new reorganization of the entire Federation as it brought all the planets within the Federation together as a more united empire.
The United Federation Starfleet, or the UFS
The beginning of the 29th century was a time for the Federation Starfleet to reorganize itself into a more cohesive power and leader for the galaxy. It was at this point that the Federation Council decided to unite the planets and it's allies into a more united organization. The name they chose was UFS, or the United Federation Starfleet.