What do decandants mean in astrology?

Like second decandant in libra?

What about Scorpio at 27 degrees? Cancer?

Each sign is divided up into decans, or groups. The first 10 degrees, second 20 degrees, then third 30 degrees. The higher up the degree, the more evolved your sign is.

For example, if you are a 1° Scorpio, that means you are just starting to learn about the lessons of Scorpio. As you move along, Scorpio is a heavy sign, and when you start transitioning to Sagittarius, the sign starts embracing adventure and new things, and starts forming their own beliefs instead of being under the dogma of fate and the world because your old sign Scorpio has gotten used to and learned about how heavy, serious, and almost restrictive it is. It starts seeing that there's a bigger world out there and so much to learn. You don't have to like the same thing over and over again obsessively and fry your brains out, you can like other things and expand your world. You can laugh instead of being so serious. And its like that with all the signs as you move along the zodiac, from Aries to Pisces and back to Aries. You'll feel it in your progressed chart.

For Scorpio, the first decan is ruled by mars/Pluto. Here's the typical Scorpio that you hear about that's very magnetic.

The second decan is ruled by Neptune. Here, Scorpio becomes a little more imaginative and artistic but still intense and all or nothing.

The third decan, where Scorpio 27 degrees would be, would be ruled by the sun. Here Scorpio expresses their ego. They like to blend in and hide. They're very sensual and touchy.

http://darkstarastrology.com/cancer-decan/

Here's a link for the cancer decans. I like using Darkstar because they're in depth and easy to understand.

Hope that helped!!!!

Each sign is divided into 3 decans, each decan has a planet that rules it that gives it its characteristics. The planet gives the "theme" of the decan