Dihydroergotamine is used to treat migraine headaches and cluster headaches. It is not recommended for migraines that affect only one side of the brain (hemiplegic migraine) or the base of the brain /neck area (basilar migraine), or to prevent migraines from occurring.
Pop music is an abbreviation for popular music. In other words, the main difference between pop music and alternative or underground music is the kind of following it has: pop music is usually known by a lot of people and regularly appears on TV.
An artist can be both 'rock' and 'pop' but the songs are what would be defined (by their mass appeal) as 'popular' - regardless of style. The difference is one that is easily reflected the numbers (of streams / downloads / sales). Pop should be considered a derivative of popular' - as noted here by others.