EXPLANATION When we write or speak, we have a range of words from which to choose. The less formal the situation, the less formal our language needs to be; the more formal a situation, the more careful we need to be with how we express ourselves. This means that we need to use a more formal register (selection, range, catalogue) of words in more formal contexts. For example, expressions such as uptight are regarded as informal slang, so in more formal contexts, we should use more formal terms such as anxious or worried.
Part of the fun of the English language is that new terms are constantly being invented, especially by young people. However, the jargon used by particular groups may not be regarded as cute or even understood by the wider community, so we should always keep our audience in mind and use appropriate language. The tenor (closeness or distance) of our relationship with our audience has to be considered as does the context.