big tent
1. noun A group, movement, or philosophy that appeals or caters to, or encompasses, the broadest and most diverse amount of members possible. We pride our church on being something of a big tent, welcoming any and all who wish to join us. The party is trying to establish itself as a big tent, broadening its aims to appeal to the widest amount of voters possible.
2. adjective (often hyphenated) Appealing or catering to, or encompassing, the broadest and most diverse amount of members possible. In my opinion, their big-tent politics, while reaching more people, dilute the potency of their goals.