Many different PVC 90 Elbow Fittings.
The 90 describes the degree. 1″, 3/4 “, 2 “, 1 1/2″ SxS means Slip by slip; slip fitting does the job of two couplings and extra pipe. Most commonly used in irrigation systems.
Spigot x Hub; Pipe and fittings have hubs into which the spigot (plain end) of the pipe or fitting is inserted. Change direction of your PVC piping using elbows.
Hub x Hub used to connect 4 in. sewer and drain (Sand D) pipe. 1 1/2” DWV, Drain, Waste and Vent.
Know your PVC. Schedule 40 has thinner walls for lower water pressure. While Schedule 80 wall thickness is for high water pressure and restricted flow. Schedule 80 is used more in industrial and chemical applications.
Schedule 40 is white, while Schedule 80 is generally gray for the purpose of identity, and possible other colors.
The inside diameter is where the two are different, along with the 80 being more expensive, and able to withstand a higher (PSI) pounds per square inch.
Tees, elbows and couplings should use the same comparable schedule.