The coconut water from a tender coconut is :

The coconut water from a tender coconut is biologically classified as a free nuclear endosperm. During the development of the coconut fruit, the primary endosperm nucleus undergoes successive nuclear divisions without the immediate formation of cell walls (cytokinesis) [t1]. This process results in a liquid tissue containing thousands of free nuclei suspended in a fluid [t5]. As the coconut matures, these nuclei and the surrounding cytoplasm begin to settle at the periphery, where cell wall formation occurs to create the solid cellular endosperm, commonly known as coconut meat [t1][t6]. While the solid white part is the cellular endosperm, the clear liquid found in the center of a tender coconut remains a multinucleate liquid endosperm [t2][t3]. This nutritive tissue provides the necessary environment for the development of the small embryo embedded within the seed [t2].

Sources

1. [1] https://pmc.ncbi.nlm.nih.gov/articles/PMC6255029/
2. [2] https://ask.loc.gov/science/faq/308429