Cheers is said while toasting, which is an act to honor the guest or the situation itself. Cheers may also be used as a greeting or a way to express thanks.
Unless you live in the United Kingdom, you mostly only hear the term cheers when you or someone else is making a toast. The toast can be honoring a person or the situation itself. Toasting and saying ‘cheers’ often includes the act or either raising our glasses in honor or by clinking the classes together. The latter is also more common for smaller intimate gatherings, rather than large formal gatherings, for which the former is used.
The most common rumor regarding the history of toasting is that people used to clink their glasses together so that some of the drink from the glass would slosh and spill into the other, thus indirectly proving that the drinks do not contain poison and that the host is not trying to poison his guests. However, there is no evidence to support this claim. Other stories claim that the noise made from clinking the glasses is said to drive the demons away, or that the clinking is a way to incorporate the sense of hearing to the act of drinking which already incorporates the other senses. However, again as nice as these reasons sound, there is no evidence to support them.
The term toasting is believed to come from the fact that a spiced piece of bread was used to soak up the acidity from the drinks and make them taste better. The drinks were then raised in honor of the guest and drunk. Eventually the term toasting came to mean the act of honoring the guest before drinking the alcohol. This act of raising their glasses to honor the guests is probably a remnant of the act of offering the food and drinks to gods before partaking in them, which was very common in Roman and Greek culture.
The act of toasting got so popular and a person would make speeches regarding every person in the room and drink in their name. This got so popular because the toast allowed a person the excuse for drinking excessive alcohol without seeming as lush or gluttonous. It was also the norm for people to finish their whole drink in the name of the person they were toasting.
Eventually, the roles of toastmasters came into existence. It was their jobs to control the environment, to ensure the toasts are being made in an expectable way and that the situation does not lead to excessive drinking. It was under their supervision that the toasting reverted back to an act honoring the guest with taking a reserved sip after the toast, rather than the debauchery that it had become.
The term ‘cheers’ came to be associated with the toast, because the term refers to cheerfulness, and good spirits, gaiety, mirth, and joy. Hence, when we say ‘cheers’ we are trying to incorporate all these feelings. However, the term ‘cheers’ is a fairly new addition to the toast. According to Merriam-Webster, the term ‘cheers’ was first used in 1919.
In the United Kingdom and Australia, as well as perhaps New Zealand, the term cheers is also additionally used as a greeting, for saying goodbye, for saying thanks, and for showing appreciation. Now, the term is getting quite popular in other countries as well.