Just like with nuts, we do not usually use the botanical definition of seeds but the culinary one.
Botanical definition: seeds are the mature ovules surrounded by a hard coat from which new plants will grow. The seed consists of the embryo, endosperm and seed coat. They are the units of reproduction of a flowering plant.
The botanical definition may be confusing if we use it in the culinary sense since the seeds in a botanical sense include food groups such as: legumes, including beans, cereals (grains), drupes, capsules, fruit such as pomegranate, spices and nuts.
In the culinary sense, seeds don’t have consistent definitions but rely on convention, depending how we eat them. On this website, seeds refers to dry seeds which are not considered nuts or legumes: