The document discusses the definition of ratios and how they relate to vectors. It defines a ratio as the comparison between two quantities that have the same unit. An example shows writing the ratio of 3000 m to 1500 m as 2:1. Ratios are related to vectors because vector problems can use ratios to determine unknown quantities, like using the ratio of 4 PS to SQ to find other vector quantities in a triangle diagram. Mastering ratios is important for understanding vectors since vector concepts apply the ratio concept.