Anything edible is considered food. Nutritional quality is another matter altogether.
Most food has its origin in plants. The fruits that plants intend for animal consumption are just the beginning. As well as parts of the plant itself, plant seeds, such as nuts and grains, are commonly eaten. ~2,000 different plants are cultivated for food. Fungi are the biggest exception to food being plant-based.
Unlike earlier Homo species, throughout history and in the world today, most people eat animals. Animals as food are categorically called seafood (mostly fish), fowl (birds) and meat (land animal flesh, mostly mammals). Insects are a food source in many cultures, while shunned in others, notably Europe and North America. Animal produce as food includes honey, eggs, and dairy.