Elbow - 2-1/2" 90 Degree SXS Sweep
2.5" Elbow 90 Degree SXS Sweep (Slip X Slip)
Sweep means it has an easier bend to ensure water is flowing properly and more consistently.
"Slip" "Slip Socket" and "Socket" all mean the same thing. The pipe glues into it. A 'female' end. The exception to this is a "Slip T" in which case the "Slip part" slides over pvc pipe.
"St" "Street" "Spg" and "Spigot" all mean the same thing. It glues into another fittings socket. A 'male' end. Note: There are both threaded street fittings and glue in street fittings. The street, spigot, st or spg just refers to the mechanism, not whether it's threaded or glued in.