A baby sling is a piece of cloth that supports an infant or other small child from a carer's body. The use of a baby sling is called babywearing. 
Ring slings can be padded or unpadded, open tail or closed tail. Unpadded slings have no padding at all, but that doesn't make them less comfortable. It does make them easier to adjust and get a good, snug fit. There is no one right way to sew an unpadded sling's shoulder because every wearer is built differently, so what's comfortable for one wearer can be less so for another. Some "hybrid" ring slings have curved seats sewn into the body, similar to the seam in a pouch. Ring slings are most closely related in use to the Mexican rebozo which uses the knot without the rings. Variation is also found in the shoulder style. Basic shoulder styles include gathered, pleated, "hot dog" or "centre fold". Ring slings are highly flexible and mostly “one size fits all" size. As long as the tail is about 8" long a ring sling is still considered safe. Tail length is decided by personal preference with most preferring the tail to hit about hip or mid-thigh.
Although the origin of mei tai is China, the variation of the traditional mei tai was popularized in Australia in the 1960s. Now, the mei tai style of carrier is becoming popular in the Western world as well, due to its supreme comfort and versatility. The meaning mei: to carry on the shoulders / tai: strap, band, they are smaller rectangle or nearly square piece of cloth with parallel padded or unpadded straps emerging from the sides of each four corner. The straps may be attached at angles or straight out or up and down. Mei tais are suitable for front or back carries with children ranging from birth to as heavy as a parent can support. The bottom straps are tied on with the fabric hanging down and then the baby is placed in position, and the top straps brought across the back or front and then brought back around to tie. It can be used on the front or back.
The podaegi also spelled podegi is a rectangle of fabric hanging from a very long strap, called a blanket (which can be wide or narrow) with one very long strap along the top edge. It can be used to hold the baby on the wearer's back, either "strapless" (with the strap tied around the mother and baby on her chest, above the breasts, and then around in back underneath the baby, and tied in front), or with the strap wrapped over the wearer's shoulders and then as above), as well as on the wearer's front, and can be used from birth onwards. Western interest in the podaegi style has led to new wrapping methods which do go over the shoulders, and to narrower "blankets". They sometimes have stiff sections which help provide head support or block wind.
The onbuhimo is similar to a mei tai, but rings are substituted where the lower straps would be. Similar to the Mei tai carriers, the onbuhimo has long top straps and a rectangular body. The rings allow the top straps to be threaded through and tightened, while the straps are tied at the waist. Variations may have stiff headrests or padding in the body. The onbuhimo is traditionally used for back carries for larger babies and toddlers. The straps may also be used "rucksack" style, more like a backpack.
Combine several features of traditional baby carriers. Usually combine the shape of a mei tai and ring sling with buckles, straps, and a padded waist belt. Can be used on front or back, structured front packs and hard-framed backpacks are also used. Most SSC are loosely based on the traditional mei tai with a main flat panels and four straps which are shortened and fitted with buckles which appeal to fathers who may not care for the tied look of other carriers.
Pouches are tube style, made with a seam in the middle, which is curved to accommodate an infant lying down, sitting up, or facing out, or an older baby in a hip carry. The seam allows the pouch sling to be as narrow as 20" wide and still be safe. They are usually not adjustable, thus comes with many sizes.
2. https://en.wikipedia.org retrieved October 10, 2015