Some sources indicate that closed-end funds are different from mutual funds, while others include them as a category of mutual funds.
For example, on one Investopedia page (http://www.investopedia.com/articles/exchangetradedfunds/08/etf-mutual-fund-difference.asp) it says "Mutual funds can typically be broken down into two types..." and lists closed-end funds along with open-end funds as a type of mutual fund. It seems like that is incorrect, but I wanted to make sure.
On another Investopedia page (http://www.investopedia.com/terms/c/closed-endinvestment.asp), it says a closed-end fund is "like a mutual fund."
A different page (http://www.investorwords.com/3173/mutual_fund.html) defines a mutual fund as "An open-ended fund operated by an investment company...":
On an SEC page (https://www.sec.gov/fast-answers/answersmfinvcohtm.html) defining types of investment companies, it says:
"The federal securities laws categorize investment companies into three basic types:
Mutual funds (legally known as open-end companies); Closed-end funds (legally known as closed-end companies); ...."