Few evolutionists would deny this hierarchy in a descriptive sense, but traditions of the modern synthesis specify that causality be sought only at the level of organisms - for natural selection operates by sorting organisms within populations.
The above quote is taken from Stephen Jay Gould's The Structure of Evolutionary Theory, a scientific text devoted to evolution. However, Gould's use of the term is vague and I have managed to identify many different meanings of it.
1) A secular "religion". Not only is the term used by creationists to create the illusion of an equal-footing, but also to create the idea that it is a religion. This furthers the same illusion and allows further, often irrelevant criticisms being advanced.
2) The nineteenth century usage. During the 19th century the term referred to people who believed that evolution had an inherent drive towards a sort of Platonic form. This view is not held today.
3) Evolution accepters. Perhaps the most common usage, this refers to anyone who accepts evolution. When referring to scientists this usage of the term is considered to be redundant.
4) Ultra-Darwinian. This usage is another used by creationists, but is more precise than imply meaning people who accept evolution. It applies to people who believe Darwinian natural selection can be used to explain more than just biological complexity and diversity. Most believe that evolution explains culture, but also have been known to explain cosmology in similar terms. Ultra-Darwinists also believe that evolution rules out the possibility of God. In this context, evolutionist is synonymous with a specific form of atheism.
5) As a profession. The term is also used simply to refer to evolutionary biologists, sounding like a portmanteau of the two words. This usage is often seen as anachronistic and redundant and so finds most use in the creation-evolution debate (though Gould's usage seems to contradict this and he was not alone).
6) Theistic evolution. Someone who accepts theistic evolution is a theistic evolutionist, though they are never referred to as simply evolutionists unless the term is being used in a broader sense.
The sixth definition can of course be dismissed as it always has the "theistic" qualifier. The second definition is outdated. The first and fourth definitions both deal with belief and are very similar, but neither is a religion in the formal sense so they can be dismissed. This leaves the term as meaning anyone who accepts it, which seems pointless, or as a profession, which is considered redundant.
It certainly appears to be a term which needs defining before it is used, unless the context is incredibly obvious. This renders the term rather useless for most situations.