What is one way to describe a bad topic sentence?

One way to describe a bad topic sentence is that it is too broad or vague. A good topic sentence should focus on a specific aspect or claim about a topic, and should be narrow enough to be manageable and specific enough to be interesting and engaging. A broad or vague topic sentence will not provide a clear direction or focus for the rest of the paragraph or essay, and will make it difficult for readers to understand what the author is trying to say.