If ray ZR is a bisector of line segment XY, it means that it divides XY into two equal parts. Since the length of XY is 10 cm, we can calculate the length of XZ as follows:
\[ XZ = \frac{XY}{2} = \frac{10 \text{ cm}}{2} = 5 \text{ cm} \]
Therefore, the length of XZ is 5 cm.