Using timer in slave mode and trigger source as ITR1

Hello I am new to stm32 MCUs. Timer1 is in slave mode and the trigger source is ITR1. What is ITR1 and in which conditions is timer generating pulses if it is in slave mode? I generated a code using mcsdk for stm32g431cbu6.

Please check line 25 in the code.

static void MX_TIM1_Init(void)
{
 TIM_SlaveConfigTypeDef sSlaveConfig = {0};
 TIM_MasterConfigTypeDef sMasterConfig = {0};
 TIMEx_BreakInputConfigTypeDef sBreakInputConfig = {0};
 TIM_OC_InitTypeDef sConfigOC = {0};
 TIM_BreakDeadTimeConfigTypeDef sBreakDeadTimeConfig = {0};
 
 htim1.Instance = TIM1;
 htim1.Init.Prescaler = ((TIM_CLOCK_DIVIDER) - 1);
 htim1.Init.CounterMode = TIM_COUNTERMODE_CENTERALIGNED1;
 htim1.Init.Period = ((PWM_PERIOD_CYCLES) / 2);
 htim1.Init.ClockDivision = TIM_CLOCKDIVISION_DIV2;
 htim1.Init.RepetitionCounter = (REP_COUNTER);
 htim1.Init.AutoReloadPreload = TIM_AUTORELOAD_PRELOAD_DISABLE;
 if (HAL_TIM_Base_Init(&htim1) != HAL_OK)
 {
 Error_Handler();
 }
 if (HAL_TIM_PWM_Init(&htim1) != HAL_OK)
 {
 Error_Handler();
 }
 sSlaveConfig.SlaveMode = TIM_SLAVEMODE_TRIGGER;
 sSlaveConfig.InputTrigger = TIM_TS_ITR1;
 if (HAL_TIM_SlaveConfigSynchro(&htim1, &sSlaveConfig) != HAL_OK)
 {
 Error_Handler();
 }
 sMasterConfig.MasterOutputTrigger = TIM_TRGO_OC4REF;
 sMasterConfig.MasterOutputTrigger2 = TIM_TRGO2_RESET;
 sMasterConfig.MasterSlaveMode = TIM_MASTERSLAVEMODE_DISABLE;
 if (HAL_TIMEx_MasterConfigSynchronization(&htim1, &sMasterConfig) != HAL_OK)
 {
 Error_Handler();
 }
 sBreakInputConfig.Source = TIM_BREAKINPUTSOURCE_COMP1;
 sBreakInputConfig.Enable = TIM_BREAKINPUTSOURCE_ENABLE;
 sBreakInputConfig.Polarity = TIM_BREAKINPUTSOURCE_POLARITY_HIGH;
 if (HAL_TIMEx_ConfigBreakInput(&htim1, TIM_BREAKINPUT_BRK2, &sBreakInputConfig) != HAL_OK)
 {
 Error_Handler();
 }
 sBreakInputConfig.Source = TIM_BREAKINPUTSOURCE_COMP2;
 if (HAL_TIMEx_ConfigBreakInput(&htim1, TIM_BREAKINPUT_BRK2, &sBreakInputConfig) != HAL_OK)
 {
 Error_Handler();
 }
 sBreakInputConfig.Source = TIM_BREAKINPUTSOURCE_COMP4;
 if (HAL_TIMEx_ConfigBreakInput(&htim1, TIM_BREAKINPUT_BRK2, &sBreakInputConfig) != HAL_OK)
 {
 Error_Handler();
 }
 sConfigOC.OCMode = TIM_OCMODE_PWM1;
 sConfigOC.Pulse = ((PWM_PERIOD_CYCLES) / 4);
 sConfigOC.OCPolarity = TIM_OCPOLARITY_HIGH;
 sConfigOC.OCNPolarity = TIM_OCNPOLARITY_HIGH;
 sConfigOC.OCFastMode = TIM_OCFAST_DISABLE;
 sConfigOC.OCIdleState = TIM_OCIDLESTATE_RESET;
 sConfigOC.OCNIdleState = TIM_OCNIDLESTATE_RESET;
 if (HAL_TIM_PWM_ConfigChannel(&htim1, &sConfigOC, TIM_CHANNEL_1) != HAL_OK)
 {
 Error_Handler();
 }
 if (HAL_TIM_PWM_ConfigChannel(&htim1, &sConfigOC, TIM_CHANNEL_2) != HAL_OK)
 {
 Error_Handler();
 }
 if (HAL_TIM_PWM_ConfigChannel(&htim1, &sConfigOC, TIM_CHANNEL_3) != HAL_OK)
 {
 Error_Handler();
 }
 sConfigOC.OCMode = TIM_OCMODE_PWM2;
 sConfigOC.Pulse = (((PWM_PERIOD_CYCLES) / 2) - (HTMIN));
 if (HAL_TIM_PWM_ConfigChannel(&htim1, &sConfigOC, TIM_CHANNEL_4) != HAL_OK)
 {
 Error_Handler();
 }
 sBreakDeadTimeConfig.OffStateRunMode = TIM_OSSR_ENABLE;
 sBreakDeadTimeConfig.OffStateIDLEMode = TIM_OSSI_ENABLE;
 sBreakDeadTimeConfig.LockLevel = TIM_LOCKLEVEL_1;
 sBreakDeadTimeConfig.DeadTime = ((DEAD_TIME_COUNTS) / 2);
 sBreakDeadTimeConfig.BreakState = TIM_BREAK_DISABLE;
 sBreakDeadTimeConfig.BreakPolarity = TIM_BREAKPOLARITY_HIGH;
 sBreakDeadTimeConfig.BreakFilter = 0;
 sBreakDeadTimeConfig.BreakAFMode = TIM_BREAK_AFMODE_INPUT;
 sBreakDeadTimeConfig.Break2State = TIM_BREAK2_ENABLE;
 sBreakDeadTimeConfig.Break2Polarity = TIM_BREAK2POLARITY_HIGH;
 sBreakDeadTimeConfig.Break2Filter = 3;
 sBreakDeadTimeConfig.Break2AFMode = TIM_BREAK_AFMODE_INPUT;
 sBreakDeadTimeConfig.AutomaticOutput = TIM_AUTOMATICOUTPUT_DISABLE;
 if (HAL_TIMEx_ConfigBreakDeadTime(&htim1, &sBreakDeadTimeConfig) != HAL_OK)
 {
 Error_Handler();
 }
 /* USER CODE BEGIN TIM1_Init 2 */
 
 /* USER CODE END TIM1_Init 2 */
 HAL_TIM_MspPostInit(&htim1);
 
}