NFP (natural family planning) and no it is not the rhythm method. You track temp, mucus, and position, and use those symptoms to determine when you are fertile. There are many methods available, but Couple to Couple League is very reliable, offers classes, and a home study option. When you actually do the charting and follow when not to have intercourse, it is every bit as reliable as hormonal birth control. Plus, there is NONE of the risk! You don't have to worry about reacting to something, long term effects, possible uterine damage, or rupture of a barrier device.
On a note to any ladies TTC, it is also great for helping you get pregnant or determine where there might be a problem with your fertility that is preventing it. We have had success using it for both routes!