Inspired by traditional Chinese baby carriers used for back carries, this style of carrier has a rectangular panel that supports the baby’s body, with a waist strap on the bottom end and shoulder straps coming off the two top corners of the body panel. They can be used to position the baby on the wearer’s front or back. There is usually no "hardware" (buckles or webbing involved) and since the waist and shoulder straps adjust by tying knots, it fits a wide range of body types and offers great support even for heavy toddlers.
Why all the different names for this one type of carrier? Here's some background information, from CatBird Baby (one of the first modern "mei tai" manufacturers based in the US)-
"Inspired by traditional Chinese baby carriers used on the back, pronounced Meh¹ Dai² in Cantonese (superscript numbers represent tones); Bēi Dài in Mandarin. Mei Tai is from an older Cantonese-English Romanization system. All transliterations are meant to communicate the same word, but use different romanizations to spell Chinese words in English, and of course many different Chinese dialects exist as well."