A picklist in Salesforce is similar to a regular picklist that you would use if you worked in a warehouse. In Salesforce, there are two different kinds of picklists. There is a single picklist and then there is a multi -picklist. Like the name suggests, a single picklist allows the user to select only one single thing or value. One answer is when this type of picklist should be used.
Some examples of where there is only one value for the picklist might include gender or age. Those only require one single value. If there is more than one value or answer to be chosen, then you should convert your single picklist to a multi-select picklist in Salesforce for your business.