In the default implementation , SysTick timer is the source of time base. It is used to generate interrupts at regular time intervals. Once HAL_ResumeTick() is called, the SysTick interrupt will be enabled and so Tick increment is resumed. This function is declared as __weak to be overwritten in case of other implementations in user file.
Examples
HAL_ResumeTick() is referenced by 216 libraries and example projects: