An action, or an instance of an action.
[French -ation or Latin -ation-. ]
The New Oxford Dictionary of English records more than 1,400 nouns that contain this suffix. Most are associated with verbs, commonly those in -ate (see -ate3): creation, deviation, moderation, navigation, perforation, pronunciation, resuscitation, suffocation, vibration. Others are associated with a variety of verbs, all ultimately from Latin: application with apply (Latin applicare); probation with probe (Latin probare, to test or prove); publication with publish (Latin publicare, make public).
Many other words in -ation appear to derive from English verbs: alteration, consultation, embarkation, formation, plantation, taxation, temptation, vexation, visitation. Though this is accidental, as the English verbs and nouns can all be traced back to Latin sources, this apparent connection was important in developing the idea of -ation as a true English suffix, so permitting nouns like flirtation to be based on English verbs. However, a number of nouns in this ending do not have an associated verb in English: duration, tribulation, ostentation, constellation.