A bloom is a flower. You might mark the beginning of spring by the very first bloom you see in your garden.
The noun bloom is useful for talking about blossoms themselves, but you can also use it as a verb meaning the process of flowering: "Those trees seemed to bloom overnight!" Another meaning of bloom is more figurative, meaning the peak or ideal moment for something. The bloom of your career selling Girl Scout cookies might be one sunny weekend outside the local supermarket. The origin of the word bloom is the Old Norse word blóm, "flower or blossom."