What is the flower.

Flower, 
a reproductive portion of any plant in the division Magnoliophyta (Angiospermae), a group commonly called flowering plants or angiosperms. As popularly used, the term “flower” especially applies when part or all of the reproductive structure is distinctive in color and form.
Time-lapse photography of various flowers bloomingEncyclopædia Britannica, Inc. Flowers function as attractors of pollinators such as beesEncyclopædia Britannica, Inc.
In their range of color, size, form, and anatomical arrangement, flowers present a seemingly endless variety of combinations. They range in size from minute blossoms to giant blooms. In some plants, such as poppy, magnolia, tulip, and petunia, each flower is relatively large and showy and is produced singly, while in other plants, such as aster, snapdragon, calla lily, and lilac, the individual flowers may be very small and are borne in a distinctive cluster known as an inflorescence. Regardless of their variety, all flowers have a uniform function, the reproduction of the species through the production of seed. The flower is the characteristic structure of the evolutionarily highest group of plants, the angiosperms.
spetuniaPink variegated flowers of a common garden petunia (Petunia ×atkinsiana).
Peter Firus, Flagstaffotos
Common lilac (Syringa vulgaris).
Courtesy of the State of New Hampshire; photograph, Ernest Gould
monster flower; titan arum; corpse flower overview of the world's largest blooms: the monster flower (Rafflesia arnoldii) and the titan arum (Amorphophallus titanum). To attract pollinators, both produce a rotting-meat scent, which has earned them the nickname “corpse flower.”
Encyclopædia Britannica, Inc.