The definition of mandala literally means "circle". It's when we define mandala in energetic terms we find that mandala meaning deals with a visual aid that pulls in the human consciousness. That's why mandalas are so effective in meditation. The circular, often concentric design of mandalas tends to visually magenetize consciousness and awareness, allowing focus to draw inward - which is a wanted result in meditation.
The above Mandala is called Mantra mandala which consists of 4 tibetan words "Om Mane Padme Hum" The first word Om is a sacred syllable found in Nepali religions and Indian religions. The word Mani means "jewel" or "bead", Padme is the "lotus flower" (the Buddhist sacred flower), and Hum represents the spirit of enlightenment.