Never heard of it before you asked, and I am guessing neither has anyone else, since you have yet to get any responses.

So I did a search and found some definitions of the acronym:

1) Small Minus Big -- One of three factors in the Fama and French stock pricing model. SMB accounts for the spread in returns between small- and large-sized firms, which is based on the company's market capitalization.

2) SMB is an abbreviation for small and medium-size business.

3) The Server Message Block (SMB) Protocol is a network file sharing protocol, and as implemented in Microsoft Windows is known as Microsoft SMB Protocol.

Wikipedia also had:

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Technology

• System Management Bus, a PC communication bus
• SMB connector, SubMiniature version B connectors for radio-frequency circuits
• Server Message Block (SMB or SMB/CIFS), network protocol
• Simulated moving bed, a variant of high performance liquid chromatography
• Surface marker buoy, a surface detection aid used by divers
• Survey motor boat, a small vessel used for hydrographic survey
• DO-214AA surface-mount diode package

Other uses

• Small and medium-sized businesses
• Michigan State University Spartan Marching Band

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Of these I am guessing that the most likely one is System Management Bus.

Of course, Stardock may have their own in house definition.

Since it deals with maps, I'm going to guess it means Super Massive Black hole.

I'm not so sure... "SMB" appears to be a feature of all of the maps. I would have assumed a super-massive black hole would be in the globular and spiral galaxies, but not the looser clusters. And I've still never seen one on a map (although the coding is in there).