Acronyms and abbreviations in avionics are special words that are made up of the first letters of other words. They are used to help quickly describe or refer to complicated or detailed things. For example, an important acronym in avionics is 'RNAV', which stands for 'Rnavigation' - which is a type of navigation system that pilots use. By using the acronym RNAV, it's much faster and easier than saying the whole thing.