What is an unimproved lane in survey? Pic included

[David Algava]

So the seller provided this survey in advance of closing.  As you can see in the image, there is a note stating "15 ft wide unimproved lane as referenced in deed, dated Dec 1818."

My agent and title aren't sure what this is. They say, probably just the HOA owns some land back there in the yard.

The whole complex was built in 1988. An unimproved lane almost sounds like a road or walkway could be allowed in the backyard. Anyone ever seen this before?  I'm sure it's not a deal killer, but still seems worth verifying.