This number refers to the end-of-year balances you entered under Household Regular Assets and how much of those assets represent unrealized long-term capital gains or losses that should be considered by our tax calculations if it is necessary to liquidate, or sell, those assets. This number should be reviewed every year when you update your end-of-year Regular Asset balances.
For example, if your regular assets have not been invested in the market using stocks or bonds, then no part of it may be a result of investment income from capital gains. This would be typical if all your regular assets are simply earning ordinary interest at your local bank in a checking or savings account. In this case you would leave the value at the default of 0.
If, however, you have your money in a brokerage account or invested in some way, the balance of that account may be due in part to growth or loss in the stock market resulting in capital gains or losses. For example, you might have a $100,000 balance at the end of last year and enter that in regular assets, but how did you get that $100K? Perhaps you got lucky or invested wisely and $15K of that was from capital gains. In other words, you invested $85K at the beginning of the year and then earned $15,000 in your funds or stocks or ETFs. That $15K is "unrealized capital gains," which simply means that if you were to withdraw it, you'd pay taxes on it at the capital gains rate. If you were to withdraw the other $85K, you'd not owe any tax on that since that was your cost basis or original investment. In this case, you would enter a value of 15000.