How would you define ERM?

ERM is about managing risks across the whole organization, as opposed to, say, one project at a time.

It is important because many of the pure risks are handled at the ERM level, not project. As a project manager, I usually don't worry about insurance or disaster recovery because it's already dealt with at a broader level.

ERM is important for companies to make strategic decisions. Each company has a different risk appetite and tolerance. ERM tells us how much risk is involved so that a company can decide if the gains outweigh the risks.