RetireJapan

I’m new to all this so please be kind.
What are the main differences between the 3 types of funds in the title?

I’m looking to invest (through Tsumitate NISA), so want to know what is available to me (I’m from U.K. but plan to stay in japan so don’t want to pay any other countries for investing).
Thanks in advance.

This information is not specific to Japan, so there are already many online resources about this. For example, from a quick search:

What's the Difference Between Mutual Funds, ETFs, and Index Funds?
Stocks Vs. Mutual Funds Vs. Index Funds Vs. ETFs: A Full Comparison

Summary:

An index fund is a type of mutual fund that tracks an index.
An ETF is a mutual fund that's traded on the stock exchange.

In Japan, your best bet is the eMaxis Slim series of index funds. They are based in Japan, and can be put into Tsumitate NISA.

Also check out https://retirewiki.jp/wiki/Japanese_global_index_funds.

Thanks for your reply.
From it, I have a follow up question.
On the wiki you posted, it noted an issue of triple taxation. Is this going to be something I’ll have to pay if I’m using a Tsumitate NISA? Which is supposed to be tax free?