If you understood the above paragraph, then you know some of the idioms and slang words and phrases used in American English. Knowing these types of words and phrases can boost your understanding and really give you an edge (give you an advantage) over those who don’t have this knowledge. Idioms cannot be understood literally. We have to memorize their meanings in order to be able to interpret them correctly. Some are easier to guess than others! It’s not hard to guess that being sick as a dog means to be very ill, but it might be more difficult to figure out that under the weather means to be sick. And scarfing down food doesn’t seem to match at all with the meaning of the word “scarf”! But a slang dictionary would tell you that scarf in this case means to eat quickly.
American idioms and slang are a huge part of American culture. While formal writing or speech does not include as many idioms or slang words, even there these words and phrases can creep in and confuse meaning for those not familiar with them.