If the assistant referee in a soccer match raises the flag, at a 45 degree angle and points it horizontally along the touch line, what does that indicate?

If the assistant referee in a soccer match raises the flag at a 45 degree angle and points it horizontally along the touch line, it indicates a throw-in.
A throw-in happens when the ball goes out of bounds over the side of the field, also known as the touchline. When this happens, the team that did not touch the ball last is awarded a throw-in. The assistant referee uses the flag to signal to the referee and the players that a throw-in should be taken.
The 45 degree angle and horizontal pointing of the flag are important signals that help the referee and players understand the decision. It is a clear and standard way to indicate a throw-in.