The current Rose classifications were introduced by the American Rose Society and edited repeatedly. These are not really clear cut. Last relevant updates from 2020:

Hybrid Tea — Perhaps the most popular class of modern roses is the hybrid tea, easily recognized by the large shapely blooms containing 30 to 50 petals. Flowers are borne on long stems either singly or with several sidebuds. In 1945, the 'Peace' rose heralded the modern era of the elegantly formed hybrid teas. So dramatic was the overwhelming public acceptance and praise accorded this variety that its place in history was instantaneous. Since 1945, many thousands of new hybrid teas have been bred and introduced.

Grandiflora - In 1954, the introduction of a rose bred from crossing the hybrid tea 'Charlotte Armstrong' with the floribunda 'Floradora' resulted in a carmine rose and dawn pink variety. It displayed not only the characteristics of a hybrid tea but also the ability to bear clusters or trusses and grow to a commanding height of 6 to 8 feet or more. To accommodate this variety, the class of grandiflora was born. 'Queen Elizabeth' had the distinction of being the very first member of this class.

Floribunda — Second only to the hybrid tea and grandiflora in popularity, the floribunda is characterized by its profuse ability to bear flowers in large clusters or trusses with more than one bloom in flower at any one time. This class is unrivaled for providing massive, colorful, long-lasting garden displays. The distinct advantage of the floribunda is its ability to bloom continually whereas the hybrid tea exhibits a bloom cycle every six to seven weeks. Floribundas as a class are hardier, easier to care for than hybrid teas.

Polyanthas are generally smaller but sturdy plants with large clusters of small 1-inch diameter blooms often used for massing, edging and hedges.

Shrub (Classic & Modern) — Shrubs are easily characterized by their sprawling habit. There are five popular subdivisions within the class: hybrid kordesii, hybrid moyesii, hybrid musk, hybrid rugosa and shrub. They can grow from 5 to 15 feet or more in every direction given the correct climate and growing conditions. Noted for their hardiness, they are usually vigorous and produce large quantities of clusters of flowers. The unique group of roses hybridized by David Austin (often called English Roses) belong to this class. They resemble old garden roses in shape and form but are recurrent bloomers and often have fragrance.