Hii Mounika!
These are the general terms, used in daily life where  we segregate eatables as vegetable and fruit. But, if we talk in terms of science, every fruit/ vegetable is a  FRUIT of its plant, originated from seed. Plant when reached reproduction stage, blooms flower. Flower gets pollinated and upon fertilisation, forms embryo. Gives rise to seed in turn. Then, the seed produces fruit having different placentation patterns. So, lemon is fruit in scientific language but a vegetable in Common language.
Hope you understand.
Good luck!