A Corporation and an S-Corporation are the same “entity” type that includes Shareholders, Directors, and Officers. The Federal government taxes each entity type differently, which is what makes each type unique.
An LLC is different from the Corporation entity type because it does not have Shareholders, Directors, and Officers. Instead, an LLC has what are called Members, which are the company’s owners. An LLC can choose “Managers” to manage and also assign titles like “President”, “Vice President”, etc. Members can be either a real person or a business entity and there are no US Citizenship requirements.
If you need help choosing the right entity type for your company, read our guide Which Business Entity to Choose.