Net Asset Value (NAV)
Commonly used to find how much a share of an ETF is worth. The NAV is found by totaling the value of all the ETFs assets and dividing by the total number of shares.
Nontransparent Active ETFs
Most ETFs are very forthcoming about what they have in their portfolio but some ETFs try to hide their investments and only show periodically as to not give away their secrets. Some ETFs choose to hide their portfolio entirely while others are using proxy portfolios which only disclose a bit of the portfolio but give investors enough to not feel in the dark.