The Meaning of $\mathbb{E}$ Operator in the Pix2Pix Loss Formula of a Neural Network / Convolutional Neural Network

I've been observing the Pix2Pix Paper - Image to Image Translation with Conditional Adversarial Networks and wondered on formulas. For example, the objective of the CGAN is: ,

where x - observed image, z - random noise, y - target image and G and D are generating and discriminating models respectively.

What does this E with "double line" stands for?

The operator $$\mathbb{E} \left[ \cdot \right]$$ is the Expectation Operator.
In the context above it means you run over all the pairs of x, y and average the values.