trilakṣaṇa (Sanskrit; Pāli, tilakkhaṇa). The three characteristics or marks of all conditioned phenomena. They are impermance (anitya), suffering (duḥkha), and absence of self (anātman). Although separate, they are also interrelated: it is because things are impermanent that they involve suffering, and it is a corollary of their impermanence that they have no enduring self or core. The implications of the three marks are set out in the first two of the Four Noble Truths.

A Dictionary of Buddhism, Oxford University Press, 2003, 2004 (which is available in electronic version from answer.com)

trilakṣaṇa[tilakkhaṇa] three characteristics of existence. Impermanence (anitya) [anicca], suffering (duḥkha) [dukkha] and non-self (anātma) [anattā] are the three characteristics of existence. 

Buddhānusmṛti - A Glossary of Buddhist Terms