The standards in the industry for a Semi-Enclosed Lav, which may also be referred to as a Partially Enclosed Lav, would not include any amenities. In most cases this would strictly be a seat within the plane that has a lift-able seat cushion exposing an emergency / chemical toilet, aka “The Potty”.
Typically located between the cockpit and passenger cabin, these chemical toilets allow for emergency use, but offer much less privacy for passengers, and do not allow you to flush. There are no doors surrounding the seat, although it may include a removable privacy curtain.
A Very Light Jet such as a Cessna Citation Mustang, Phenom 100, and Cessna Citation Jet, along with some Turbo Props like the King Air 90, are some of the most cost-effective aircraft on the charter market.
These aircraft types feature “Potties” instead of fully equipped bathrooms, and many clients don’t mind exchanging the privacy of a fully enclosed lav for a more cost effective option.