What exactly are PL, PLL, PLC, PLT, PLS, PLR, PLH, PLQ lamps?

PL lamps are plug-in fluorescent lamps and became widely known since Philips marketed its PL series non-integrated compact fluorescent lamps including PL-L, PL-C, PL-T, PL-S, PL-R, and PL-Q. They often appear in other variations: PLL, PLC, PLT, PLS, PLR, PLH and PLQ.

PL-L stands for plug-in lamps in long version.
PL-S stands for plug-in lamps in short version.
PL-T stands for plug-in lamps with triple compact fluorescent turns (3U).
PL-C stands for plug-in cluster fluorescent lamps.
PL-R stands for radius model (round socket) plug-in lamps.
PL-H stands for high output plug-in lamps.
PL-Q stands for Quadrant (2D) shaped flat lamps.

PL lamps are available in various forms of 2-pin or 4-pin bases, including G-23, GX23, GX23-2, G24d-1, G24d-2, G24d-3, GX32d-2, G24q-2, G24q-3, GX24q-2, GX24q-3, GX24q-4, 2G8-1, 2G11, GX24q-5, and GX32d-3. LED PL bulbs are designed to retrofit inefficient compact fluorescent lamps (CFLs) with hassle-free installation.