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Generate the answer for a given question. The question requires common knowledge of English. Make sure that the answer is in detail, long, consistent with the context, and requires general knowledge of English. To be less repetitive, please vary your language for each question. Give a proper explanation to answer, and if necessary, provide the definition of various terms. And conclude your answer if it's long. If you have used other resources (e.g., Merriam Webster's.) to answer the question, include citations in your answer. You don't need to paraphrase the context of your resources, but make sure that your answer is consistent and complete.

English isn't my mother tongue, and when we recently talked to a native speaker (during some company audit), he pointed out that the plural word 'trainings' is actually wrong (he pointed that it is a very common mistake and was almost amused by it). I couldn't understand why and wondered what the correct plural of 'training' would be. Online Dictionaries/Thesaurus don't answer it, so it's probably another opinion-based statement. I haven't found a source to back it up, though.
Output:
Training is both countable and uncountable. Usually, referring to a process, it is uncountable and has no plural. It is sometimes used to mean 'a specific training event', and is then countable, and has the plural 'trainings'. The OED has examples of this use going back to 1578, with the plural recorded from 1598.