In the "Estimate" column for my American Community Survey (ACS) table, I see a value of "0." Does this mean that no one in the population had that characteristic?

A zero estimate in the data table means no respondent that was surveyed had that characteristic for the geographic area of interest. The ACS is a survey that is sent only to a subset of the population; therefore, not everyone in a geographic area is surveyed. It is possible there are persons in the population who possess that characteristic that were not sampled. This is why the ACS includes a margin of error, which means there is a 90% probability the true value may be as large as the margin of error for the zero estimate.