"ISTG" stands for "I swear to God." It is an acronym commonly used in texting and online communication to emphasize the seriousness, truthfulness, or intensity of a statement. People often use it to assure others that they are not joking or to express frustration, surprise, or exasperation. Despite the phrase containing a religious reference, it is typically used casually and not in a religious context

. Examples of how "ISTG" is used include:

• "She asked him out after practice, ISTG I'm not lying."
• "ISTG if they kill off my favorite character this season..."
• "ISTG, this homework sucks."
• "ISTG, if you don't turn down your music, you're grounded."

The acronym helps convey earnestness or annoyance and is popular among younger people in informal communication