C# interface is kind of like Rust's trait except the default passing convention by interface is similar to Box<dyn Trait> whilst passing structs implementing interface via generic arg is identical in the form of Accept<T>(T value) where T : ISomeInterface.

Arguably, today the line is somewhat blurred because interfaces can have default member implementations (which are used to extend interfaces without making it a breaking change) but generally you are correct. An abstract class and subclasses that inherit from it signifies what the type is while the interfaces a class or struct implements signify what the type does.