什么是 SP Socket？

学习 nanomsg 时候看到的，谷歌上查了以下，没怎么看懂，我贴在下面：

DP = double pole = makes/breaks both phase and neutral.
SP = single pole = makes/breaks phase only.

Read more: https://www.diynot.com/diy/threads/sp-or-dp-sockets-whats-the-difference.97625/#ixzz7LgVidGWE