parenchyma

noun

1. Anat. the essential or functional tissue of an organ, as distinguished from its connective tissue, blood vessels, etc.
2. Bot. a soft tissue made up of thin-walled, undifferentiated living cells with air spaces between them, constituting the chief substance of plant leaves and roots, the pulp of fruits, the central portion of stems, etc.
3. Zool. a spongy mass of tissue packing the spaces between the organs of some invertebrates