The abbreviation 'btw' stands for "by the way." It is often used in casual conversation to introduce a new topic that may not be directly related to the previous discussion. It's a way to add information or a side note without changing the main subject of the conversation.
The term 'btw' is derived from the phrase "by the way," which has its roots in Old English. The phrase began to be used more prominently in the 19th century as people started to engage in informal conversation. The abbreviation gained popularity with the rise of the internet and texting, making it easier to communicate quickly.