What is a personal foul, and what happens after three?

Under World Aquatics rules (Part Six, Article 17):

• A personal foul is recorded against a player every time they commit an exclusion foul or a penalty foul. Ordinary fouls don't count.
• The Referee shows the player's cap number to the secretary, who records it.
• A player with three personal fouls is excluded for the rest of the match and must leave the field of play straight away. The secretary signals the third personal foul with a red flag.
• If the third foul was a penalty foul, a substitute may come in immediately. Otherwise, the substitute comes in on the normal exclusion re-entry (18 seconds of play, a goal, or when the team regains the ball or is awarded a free throw, goal throw or penalty throw, whichever is first).