Generate a topic word for the given sentence. A topic word is usually the name of a person, place, animal, concept or object the sentence is focusing on.

goldenrods are any of the about 150 species of weedy herbs that make up the genus solidago.
goldenrod

absolute truth is something that is true at all times and in all places.
absolute truth

escape velocity is the initial speed that something would need to completely escape the gravity of a large body, like a star or a planet (such as the earth), by mere inertia.

escape velocity