What does MR version stand for?

Today I got Android ICS update. The system shows version "Ice Cream Sandwich MR1". I know alpha, beta, rc, rtm, etc. but I was wandering what MR stands for.

What does Mr mean in software?

The Wikipedia view: Mixed reality (MR)—sometimes referred to as hybrid reality—is the merging of real and virtual worlds to produce new environments and visualisations where physical and digital objects co-exist and interact in real time.

What is Mr release?

MR (modified Release) is the general term for all the drug delivery systems that are deviating from the conventional release pattern, these include all the preparations known as SR, CR, XL.

I think it means Maintenance Release 1.

Source: I just heard it somewhere on a different application using MR in their version.