I don't know where your pulling your data from (as in what website or software) but normally the word assessed is referring to the tax assessed value, or the the value the county tax collector / assessors office places on the subject property to determine how much to charge in annual property taxes.
Often the tax assessed value is not an accurate representation of market value but it depends on the state.
Appraised total value is probably (I'm guessing here) the software's or website's attempt at estimating the market value of the subject property based on an algorithm they put in place.
These are rarely accurate for land, so I wouldn't put much stock in them.
Hope that helps!