Seed is an embryonic plant enclosed in a protective outer covering. The formation of the seed is part of the process of reproduction in seed plants. Seeds have been an important development in the reproduction and success of gymnosperms and angiosperms plants, that now dominate biological niches on land. 

The term "seed" also has a general meaning of anything that can be sown, e.g. "seed" potatoes (tubers), "seeds" of corn or sunflower "seeds". 

Many structures commonly referred to as "seeds" are actually dry fruits. Different groups of plants have other modifications, the so-called stone fruits (such as the peach) have a hardened fruit layer (the endocarp) fused to and surrounding the actual seed.

Nuts are the one-seeded, hard-shelled fruit of some plants with an indehiscent seed (acorn, hazelnut).