As far as I understand, Merkaba is a word of Egyptian origin. ‘Mer’ means a light that rotates within itself, ‘Ka’ means spirit, and ‘Ba’ means the physical body.
Merkaba is an energy field that can be activated or awakened through meditation. It is said to elevate you to a higher consciousness and take you beyond the limitations of daily life.
This energy field as an interesting sacred geometry which is explained in detail here.
Here is a guided audio meditation on Youtube of a Merkaba meditation:
It is from the book The Ancient Secret of the Flower of Life, Volume 2 by Drunvalo Melchizedek. It is claimed that this kind of meditation can change your consciousness to a higher dimensional awareness of peace, love and harmony.