Soft Structured Carriers (aka Buckle Carriers) Is a type of carrier that buckles onto you. The carrier consists of a body (the panel of fabric where baby goes), a waist strap, and two arm straps. These Carriers are normally pretty heavily padded in the waist and shoulders for added support.
SSCs tend to be thought of as a more 'mainstream' carrier. This makes them easier to find in chain stores such as Babies R Us, Walmart, and places like TJMax and Marshalls. The simplicity of them makes them a favorite among many parents. Buckle carriers aren't nearly as daunting as some other choices like wrapping. They are quick and easy. A lot of SSCs are capable of front, hip, and back carries such as the Ergo.
The difficult things about Buckle Carriers is that they have sized bodies, so usually its not a one stop shop. You'll need a regular standard sized one, some type on infant insert, a Toddler size, and a preschool size if you continue wearing an older or bigger baby. It can also be difficult to find a good fit for the wearer. They do have webbing that adjusts but sometimes they don't don't go small enough or big enough. Some brands have extra accessories to combat this like waist extenders or perfect fit adjusters (they make the arm straps smaller). However once you find a good fit for baby and wearer they are amazing!