After the rebranding of Twitter to "X" in 2023, a "tweet" is now officially called a "post."
A subtweet is a tweet about a person that doesn't mention their username with the @ symbol. For example, if someone tweeted, "Hey computerhope, I need help," we would not be notified because it's missing the @ symbol in front of our username. However, we would be notified if the tweet was "Hey @computerhope, I need help."
If your username is unique enough, you could also use the Twitter search to find any tweet containing your username.
What is the character limit for a tweet?
The character limit for messages on Twitter is 280 characters.