pollen grain

It depends on whether you are talking about animals or plants. In plants it is a pollen grain (microgametophyte) and in animals is a sperm (spermatozoa)

Unlike seedless vascular plants gymnosperms do not require water to transport the sperm. Instead a partly developed microgametophyte (pollen grain) is transferred to the viscinity of the megagametophyte (female) passively by the wind this process is called pollination. After pollination the endosporic microgametophyte produces a pollen tube and drops the sperm into the female ovary (i believe this is called pollination drop).

it depends on gymnosperm (naked seed) or angiosperm (flowering plant) this is the angiosperm - Another germination event during the life cycle of gymnosperms and flowering plants is the germination of a pollen grain after pollination. Like seeds, pollen grains are severely dehydrated before being released to facilitate their dispersal from one plant to another. They consist of a protective coat containing several cells (up to 8 in gymnosperms, 2-3 in flowering plants). One of these cells is a tube cell. Once the pollen grain lands on the stigma of a receptive flower (or a female cone in gymnosperms), it takes up water and germinates. Pollen germination is facilitated by hydration on the stigma, as well as the structure and physiology of the stigma and style.[1] Pollen can also be induced to germinate in vitro (in a petri dish or test tube).[3][4] During germination, the tube cell elongates into a pollen tube. In the flower, the pollen tube then grows towards the ovule where it discharges the sperm produced in the pollen grain for fertilization. The germinated pollen grain with its two sperm cells is the mature male microgametophyte of these plants.[1

The angiosperm life cycle begins with a diploid (2n) flower on the mature sporophyte plant. Within the anther, the microsporocytes develop and undergo meiosis (reduction of chromosomes) to produce haploid (n) microspores. Each of these undergoes one mitotic division to produce a generative cell and a tube cell. Together they make an immature microgametophyte, or pollen grain. The generative cell completes a second mitotic division to produce two sperm nuclei. Inside the ovule a single megasporocyte develops, undergoes meiosis, and produces four haploid (n) megaspores. Three of these die off, while the fourth undergoes three mitotic divisions to produce an eight-nucleate embryo sac, or mature megagametophyte. Upon pollination, the pollen grain germinates on the stigma, a pollen tube grows down the style and into the ovary through the micropyle. One sperm nucleus fuses with the egg to create a diploid (2n) zygote, while the other sperm nucleus fuses with the two polar nuclei to produce the nutritive, triploid endosperm. The embryo develops inside the embryo sac, integuments of the ovule form a protective seed coat around it that provides protection and nutrients. The seed is then shed from the fruit and the development of the embryo is temporarily halted until the proper conditions are established. Once the proper conditions are established seed germination takes place and the embryo grows into a mature diploid (2n) sporophyte, which produces flowers and completes one cycle of the alternation of generations.