MRM removed from the all ordinaries index

The news of MRM being removed from the all ordinaries index had me intrigued. What does that mean. Well I looked it up and below is the definition

Established in January 1980, the All Ordinaries (colloquially known as the "All Ords"; also known as the All Ordinaries Index, AOI) is the oldest index of shares in Australia. It is made up of the share prices for 500 of the largest companies listed on the Australian Securities Exchange (ASX).^[1]The market capitalization of the companies included in the All Ords index amounts to over 95% of the value of all shares listed on the ASX. The 3-letter exchange ticker in Australia for the All Ordinaries is "XAO".