The "16x" indicates a 16x16 pixel resolution. This is the standard Minecraft resolution, making the pack lightweight and ideal for maximizing frames per second (FPS) on lower-end PCs.
You can find demonstrations and download links for versions like the Spreen 40k 16x Full FPS Pack or earlier Spreen Mashup packs on YouTube and community texture pack sites. spreen 40k 16x
Clear skies and "low fire" textures that help in UHC and PvP scenarios. The "16x" indicates a 16x16 pixel resolution