Level streaming is the technique of loading and unloading sections of a game world dynamically as the player moves through it, rather than loading everything upfront or showing loading screens between areas. The game predicts where the player is heading and begins loading those assets from disk into memory while simultaneously unloading areas the player has left behind. The engineering challenge is doing this without causing frame rate hitches, which requires careful priority management of I/O operations, background decompression, and memory budgeting. Modern open-world games would be impossible without level streaming -- you cannot fit an entire Skyrim or GTA map in memory at once. SSDs have been transformative for this technique because faster read speeds allow streaming to happen closer to when the player actually arrives.