2. A fleshy, protein-rich "food patch" on some seeds or fruits which is attractive to ants and so aids the dispersal of the seeds.
The elaiosome is rich in lipids and proteins, and may be variously shaped. Many plants have elaiosomes to attract ants, which take the seeds to their nest and feed the elaiosome to their larvae.
After the larvae have consumed the elaiosome, the ants take the seed to their waste disposal area, which is rich in nutrients from the ant frass (fine powdery material phytophagous or plant-eating insects pass as waste after digesting plant parts) and dead bodies, where the seeds can germinate.
This type of seed dispersal is termed myrmecochory, from Greek myrmex, "ant" and kore, "dispersal" and is discussed in more detail at the link indicated in this sentence.
Stimulated by the attractants, the ants transport the seeds to new locations, discard them after feeding on the elaiosomes, and so aid in the dispersal of the seeds.