What is glass called that looks mirrored but doesn't reflect distinct images?

Reflective

Cylinder glass - which is blown in a long cylinder which then has the ends cut off and is cut down the side and opened in a kiln - will have ripples because of the different circumference of the inside and outside. If a mirrored surface is applied to the back (or paint for a more muted effect) the images will behave as you describe. http://www.mikegigi.com/winlight.htm

Cylinder glass as a main method of making window glass ended about 1900 when continuous drawn glass making started. This produces a slight ripple - like the windows in my house built in the 1920's

Float glass, developed in the 50's, produces glass without ripples.

I believe you're refering to Mercury Glass.