[Yageo's SMT capacitor datasheet](https://www.yageo.com/upload/media/product/productsearch/datasheet/mlcc/UPY-GPHC_X7R_6.3V-to-50V_18.pdf) lists the ESR vs. Frequency Curve show below:

[![enter image description here](https://i.stack.imgur.com/9EQQ0.png)](https://i.stack.imgur.com/9EQQ0.png)

Note that impedance (Z) is listed in units (W). How can this be understood? Why is impedance seemingly not measured in Ohms, as is customary?