I was looking at some mutual funds that list amounts for "initial" and "subsequent" investments under the "minimum investment" category. At first I thought that the "subsequent" requirement meant that you had to invest at least that much every year or month. I looked around online to try to find a good explanation of what it was, but couldn't find anything that directly explained it. However, I'm inferring from what I read that it simply means that if you ever do invest more money in the fund, they want you to do it in chunks at least that large (presumably so they don't have to process tons of small transactions). Is this correct?
It costs money for a mutual fund to accept your money. It doesn't cost as much as it used to, but historically there has been, at a minimum, a modicum of record-keeping associated with it. As such, they will typically have a minimum amount of money they want you to add at a time. They don't want to process 100 transfers of a nickel each; that would be silly.
So if you have a mutual fund with a "minimum initial investment" of $10,000 and a "minimum subsequent investment" of $100, then that means that you can put in $10k to open it, and then deposit dollars in lots of 100 or more whenever you feel like it.