"Bitcoin ETF" refers to listed investment trusts that include investments in Bitcoin.
"ETF" is short for "Exchange Traded Funds." It refers to investment trusts that are listed on stock exchanges. Since these securities companies are listed on exchanges, it is possible to trade through them in the same way that people buy and sell stocks.
A mutual fund is a product where money from investors is collected in a single fund and invested in stocks, bonds, etc. by a specialist.