Mei Tai's are soft carriers with a back panel for baby, and waist / shoulder straps to secure the carrier in place. They are fairly similar to buckle carriers but straps are secured by tying a knot rather than being clipped in place.
Mei Tai's are usually more versatile than a buckle carrier, as they can be tied in a variety of ways. Front, back and hip carries are usually achievable. Shoulder straps can be crossed to increase support in a front carry, or (dependent on length) can be tied at the chest in a back carry (great for those wearing while pregnant or those who prefer baby's weight to be higher on their body).