Wikipedia
In English, the country is popularly known by either of its short names "Burma" or "Myanmar". Both these names are derived from the name of the majority Burmese Bamar ethnic group. Myanmar is considered to be the literary form of the name of the group, while Burma is derived from "Bamar", the colloquial form of the group's name.
Originally Posted by
freezefactor
My understanding is that the term Myanmar is more inclusive of other ethnic groups, whereas Burma refers to the Bamar ethnic group.