The term "tysm" is an abbreviation commonly used in informal communication, especially in texting and online messaging. It stands for "thank you so much." It expresses a deeper level of gratitude than just a simple "thank you," indicating that the speaker is very appreciative of someone's help or kindness.
"tysm" originated from the phrase "thank you so much," which itself has roots in the Old English word "þanc," meaning "thought, gratitude," and the word "so," derived from Old English "swā," expressing degree. The abbreviation likely gained popularity with the rise of texting where brevity is preferred.