First, lets define frameless shower doors. Frameless shower doors use hinges, clips and corner brackets to secure the glass leaving the entire edge of the glass uncovered, hence frameless. Certain frameless shower glass systems require a top metal support plate to secure the glass properly.
Pictured above is a Frameless Shower Glass Enclosure with a sliding door.
Semi-Frameless Glass shower enclosures are much different. These systems typically are frameless glass with a metal framing around the entire structure. Semi-Frameless Glass enclosures are typically less expensive than frameless systems because the glass is thinner and has less luxurious look and feel.