Assimilation is the process of incorporating nutrients or other molecules into the body of the assimilating organism.
Plants for instance, readily assimilate nutrients from their surroundings. It is slightly different to 'feeding' in the normal sense; obtaining nutrients by feeding involves a complex process of breaking down the food into its constituent parts, which can then be used to form other substances, or discarded as waste. In assimilation, the molecule being assimilated is transferred directly into the body of the organism and used in its entire form as a part of the body. Assimilated molecules, or objects, become a part of the organism that has assimilated them.