1. Prayer is: (a)either asking of God to do sth.(b)thanking God For sth.(c)or glory God. Meditation is letting the Divine to address you. 2.One categorization could be
a)the tense posture, where the body is forced to keep a straight vertical position of the spine,(Hindu & Buddhist Yogi's)(b)the more relaxed posture (Tao meditation of China) Although a better categorization is: meditating lien, sitting, standing, in motion, and during sex. 3.The effects vary between relaxation and intense spiritual experiences. Always best to have an authentic instructor. My piece of advice to someone who starts meditation is:Even if you see God telling you: ''You Are The One''... don't ..