The concept of an "unrealized holding" is borrowed from traditional accounting. With cryptocurrency, unrealized holdings are simply the crypto assets that you purchased, but did not sell, prior to January 1 of the tax year you are currently working on. These are considered "unrealized" in our system as they have not been sold for a gain or loss.
Lukka may also refer to "unrealized holdings" as "roll-forward" or "starting balance."
You are working on your 2019 taxes, and you purchased bitcoin in 2018 but had not yet sold it as of the start of 2019 (1/1/2019). The bitcoin you purchased in 2018 would be unrealized holding and should be entered on the corresponding page in Lukka.
NOTE: Lukka does not provide tax advice. The statements above are general in nature and do not address how the application of the tax rules can vary based on a taxpayer’s actual facts. Please consult a tax professional on how the tax rules apply to your specific facts.