The concept of supply and demand is an economics concept you may have learned in a basic economics class in high school or college. Can it be applied to closed end funds?. You buy and sell closed end funds at the market price (sell at the bid and buy at the ask). Do closed end funds have NAVs? (net asset value per share). Yes, but you can't transact at the fund's NAV. On a closed end fund, the market price may rise above the NAV, which would be called a premium and the market price can fall below the NAV, which would be called a discount.
Back to supply and demand in the closed end fund world. The concept here is really not all that different from why stock prices move. If investors really like the closed end fund or stock as evidenced by a lot of buying, the market price goes up. If investors think the closed end fund or stock is terrible, as evidenced by a lot of selling, the market price falls.