Live rosin starts with fresh frozen buds (no drying/curing). The process uses water, heat and pressure to extract the plant resin.
Most smokable rosin products are divided into 90u and full spectrum. During processing, the hash is filtered through mesh bags. 90u refers to the size of the hole in the mesh bag - when products are labeled 90u, they are only from this single bag. The 90u is considered the cream of the crop.
Full spectrum products come from multiple wash bags. While this can sometimes produce a darker color rosin, taste and smell are extremely comparable to 90u when a high quality processor is involved.