Experiential and Volitional Nihilism
Meaning in life is generated by the realization of values. Values can be experienced, both actively and passively.
Nihilism is the position that all values are baseless. It doesn't simply declare that values do not exist, but rather that they exist only within the realm of human subjective experience, and that there is no such thing as meaning or value outside of it in the objective reality.
Based on this, I can differentiate between two strains of nihilism:
1) Experiential Nihilism, which is an inability to experience values and thereby an inability to experience meaning.
2) Volitional Nihilism, which is a refusal to realize values. When confronted with the possibility of meaningfulness, a volitional nihilist would respond that even if values can be experienced and meaning can be generated, why bother, it is all an illusion and a deception anyway.
Experiential Nihilism can often be the result of a pathological (for lack of a better adjective) state of mind, such as a person suffering from major depression. An experiential nihilist simply does not have access to an experience than others have access to. Volitional Nihilism, in turn, can arise out of rationalization of experiential nihilism (but not always and not necessarily).
However, underlying Volitional Nihilism is a cloaked value judgement: it is the belief that truth is always preferable to consolatory illusions, and the truth as perceived by nihilism is that the reality is devoid of meaning and value. And yet, if there genuinely are no values, there is no reason to prefer truth over falsehood. Even the nihilist cannot rid himself of the value of truth.