The trust score is a risk measure. It measures the likelihood of a project not being legitimate based on a number of parameters.
A grade "A" means that we have done extensive KYC, that we have checked certain data and other characteristics of the project and that we are relatively comfortable that it carries a low risk of being fraudulent.
A grade "E" means that either we did our checks and the project scored very low or that we have not yet done the checks. Either way, from our system's perspective this project is more risky than an "A" project.
Also note, that these scores are for informational purposes only. Everyone should always perform their own research and make up their own minds when it comes to joining projects and investing funds.