The process of two cells combining is called fertilization in the context of sexual reproduction.

Here's a breakdown:

* Fertilization is the process where a sperm cell (male gamete) and an egg cell (female gamete) fuse together to form a zygote.

* This zygote contains a complete set of chromosomes, half from each parent, and has the potential to develop into a new organism.

While fertilization is the most common term, there are other related processes:

* Fusion is a more general term that describes the merging of any two cells, not just gametes.

* Syngamy is a synonym for fertilization, specifically referring to the fusion of gametes.

Let me know if you have any other questions!