The mlflow.start_run(run_name='Run name') function is used to initiate the tracking of a new MLflow run with a specified name. This function creates a new entry in the tracking database to record all the information (parameters, metrics, artifacts) associated with this specific run. The run_name argument allows you to assign a meaningful name to this run for better organization and identification later. Other options are incorrect because:

• Creating a new experiment is not the primary function of this call; it creates a new run within an existing experiment.
• It does not just modify the name of an existing active run; it creates a new run.
• Logging metrics is done within the active run context using separate mlflow.log_metric calls.
• While you can start a new run without specifying a name, providing a descriptive name is recommended for better organization.