The ability of a good or asset to be exchanged with other goods or assets of the same value. For instance, money is a prime example of a fungible asset, in the sense that a $1 bill is convertible into 4 quarters. Goods and assets that are non-fungible are assets that aren’t interchangeable, like owned cars and houses. Shares of stocks that are listed on multiple exchanges (or cross-listed stocks) are still considered fungible.
We don't know everything about the markets. We're just devoted to learners. Taken from those smarter than ourselves, here's how we define Fungibility.