It tells you what the paragraph is going to be about.
An F1 hybrid (or filial 1 hybrid) is the first filial generation of offspring of distinctly different parental types. F1 hybrids are used in genetics, and in selective breeding, where it may appear as F1 crossbreed. The term is sometimes written with a subscript, as F1 hybrid.
A hybrid vehicle is a vehicle that uses two or more distinct power sources to move the vehicle; for example, a conventional internal combustion engine and also a high voltage electric motor. series-or serial-hybrid vehicle is driven by an electric motor, functioning as an electric vehicle while the battery pack energy supply is sufficient, with an engine tuned for running as a generator when the battery pack is insufficient.