In Hinduism, the ‘tilaka’ is a mark usually worn on the forehead, but sometimes other parts of the body such has the neck, hand or chest. It can be worn daily for rites of passage or special religious occasions, depending on regional customs. Different Hindu traditions use different materials and shapes to make the ‘tilaka’, created by the application of powder or paste appearing on the forehead as a vertically shaped marking.

The term also can refer to the Hindu ritual of marking someone’s forehead with a fragrant paste, such as from sandalwood or vermillion, as a welcome and expression of honor when they arrive. This tradition is a cultural gesture often seen in India and Nepal (picture).

The choice, style or type of ‘tilaka’ is not mandated by Hindu texts, but is left to the individual and the regional culture, leading to many versions.

In contrast to ‘tilaka’, ‘bindi’ is a Hindi word, also from Sanskrit meaning ‘point, drip, dot or small particle’. As seen on the individuals’s forehead, it will appear as a colored dot in the center.

‘Om’ symbolizes the universe and the ultimate reality. It is the most important Hindu symbol. It is part of the iconography found in ancient and medieval manuscripts, temples, monasteries and spiritual retreats in Hinduism, Buddhism, and Jainism.

‘Chakra’ refer to the various focal points in the ‘subtle body’ (a series of psycho-spiritual living beings) used in a variety of ancient meditations.

More Info: en.wikipedia.org