Trines (120 degree angles) form between planets of the same element (Air, Fire, Earth or Water) and they form an understanding. They communicate very well together.
Trines are harmonious, each one encouraging the other to get active and stimulated. The only negative about trines is that they sometimes are too comfortable together, and need your support in order to get back to motion.
Aspects are angles created by the varying positions of the planets in the sky in relation to one another.