Philanthropy is the act of donating money, to try and bring about some goal in the world. On LessWrong, the topic tends to include an assumption of "you are spending money to optimize for a goal, rather than just signal tribal affiliation.
Disambiguation: Effective Altruism is a social movement focused on how to do the most good, which includes how to optimize philanthropic giving. The Effective Altruism tag tends to focus on the social movement, and the philanthropy tag tags to focus on the specific question of "how to optimize the giving of money"