“Multi Roblox” usually means running more than one Roblox client — multiple windows, multiple accounts — on the same PC. Search terms like multiroblox, multiple Roblox instances, and 2 accounts at once all point at that workflow.
The official Roblox client is one session at a time per login. MultiRoblox helps you start additional instances from a Chrome panel so you can play on two accounts at the same time.
Related guides: how to run multiple accounts · account manager overview