An index fund is a type of mutual fund with a portfolio constructed to match or track the components of a market index, such as the Standard & Poor's 500 Index (S&P 500). "Indexing" is a passive form of fund management that has been successful in outperforming most actively managed mutual funds.
In other words, an index doesn't actually exist in a sense. Rather, it is an academic concept; an idea. Basically, it amounts to a person or a committee of people sitting down and coming up with a list of rules as to how to construct a portfolio of individual holdings because, in the end, the only thing you can actually do is invest in individual common stocks or bonds, presuming we're limiting our discussion to equity and fixed income markets.
Including ten cryptocurrencies was our first approach for the index, however we thought that we were overlooking some interesting projects currently ranked in the 11th - 30th range, so even if the market capitalization of these coins is lower than the top 10 cryptocurrencies we felt they deserved to be part of the index since they have a lot of growth potential, we incorporated these coins with less weight on the CryindexFund.
If we added the total market cap of the top 30 cryptocurrencies, we would obtain the total market capitalization of all of them. If we were to use the respective percentage of each cryptocurrency in the top 30 to define which part of the index they should have, we would end up with an index moving in parallel with Bitcoin which represents around 80% of this total market cap of all these coins.