The label is displayed in a picklist field on a record, and the API name is used everywhere else. For example, data import and export and Apex code use the API name.
You can prevent users from changing a picklist value’s API name. From Setup in Salesforce Classic, enter Picklist Settings in the Quick Find box, and then select Disable editing picklist values’ API names. You can only access Picklist Settings from Salesforce Classic.