The blast radius of an explosive was the area it could be expected to affect.
In 2346, Halb Daier assured "Luma Rahl" that a bomb which she was going to plant on Terok Nor had a blast radius of twenty meters, and that it should be set down in Gul Dukat's quarters. (DS9: "Wrongs Darker Than Death or Night")
In 2375, Kathryn Janeway told Tuvok that USS Voyager could not clear the blast radius of an explosion without warp drive. (VOY: "Juggernaut")