The meaning of a cat with an erect tail can vary depending on the situation and the individual cat. Here are some common explanations:

Confidence and alertness: When cats feel confident, alert, or in a state of alert, they may erect their tail Lift the tail. This can indicate their attention to their surroundings and their readiness to respond to potential threats or stimuli.

Excited and active: Cats may also raise their tails when they are excited, active, or ready for action. For example, when they see prey, are ready to play, or are interested in an activity.

Social signals: A cat's erect tail may be a social signal during interactions with other cats or humans. It can indicate friendliness, closeness, or interest in other cats.

Uneasy or nervous: In some situations, a cat with a raised tail may also indicate uneasiness, nervousness, or uncertainty. This may be a reaction to new surroundings, strangers, or other situations that make them uncomfortable.