A cold stream does not start producing values until one starts to collect them. A hot stream on the other hand starts producing values immediately.
I would recommend to read below to understand hot and cold steams with usage:
https://balwindersinghrajput.medium.com/complete-guide-to-livedata-and-flow-answering-why-where-when-and-which-6b31496ba7f3
https://developer.android.com/kotlin/flow/stateflow-and-sharedflow