What is the meaning of free leech?

[F] symbol is used to indicate that a torrent is subject to Freeleech.

When a torrent is flagged with this symbol, it means leeching that torrent will not affect your download amount and will not decrease your ratio. Meanwhile seeding that torrent will continue to improve your ratio and will increase your upload amount. This is an Excellent way to improve your ratio.

Torrents with specific type of content are subject to Freeleech, this is to promote their distribution.