The noun for the act of transgressing — a crossing of a line you should not have crossed. It is countable when you mean one particular act ('a serious transgression', 'his early transgressions'), and uncountable when you mean the behaviour in general ('a life of transgression'). Formal, and often moral or religious in flavour: in the Bible and in sermons, 'transgressions' are sins, and the word carries that weight even outside church. In news writing it is a polite, slightly distancing way to name someone's wrongdoing — 'the minister's financial transgressions' sounds gentler and more official than 'the minister's cheating'. In art and literary criticism it has the other life the verb has: 'transgression' there can be a positive project, the deliberate breaking of taboos. Common shapes: 'a transgression of the rules', 'commit a transgression', 'forgive someone's transgressions'. In ordinary conversation people simply say 'mistake', 'wrongdoing', or 'what he did'.