The expression $P(E|M)$ represents the conditional probability of event $E$ (landing on an even number) given that event $M$ (landing on a multiple of three) has already occurred. In other words, it's the probability that the number cube shows an even number, assuming that it is already known to be a multiple of three.

Do you have any questions about this? Here are 5 related questions to explore further:

1. What are the possible outcomes when rolling a fair six-sided number cube?
2. How would you calculate $P(E|M)$ for this specific problem?
3. What is the probability of landing on a multiple of three when rolling the cube?
4. Can a number be both even and a multiple of three on a six-sided cube?
5. How does the formula for conditional probability work in general?

Tip: When solving conditional probability problems, it's helpful to list out all possible outcomes that satisfy the condition first.