What is designated at fair value means?
you have an available for sale designated security. you bought it at some price (your value). over time the security undergoes changes in market value due to change in price. each time a change in price occurs - you take a gain or a loss on your income statement - and then “adjust” the value of the security to its “fair value” - which is the adjusted value (accounting for the gain or loss) on your income statement.
now if you decided to sell it - you would sell it at the “fair value”.
Fair value - a price at which the buyer is willing to sell and at which a seller is willing to buy in a arms-length transacation without any coercion.