Anything you use to call someone's attention. It can be a literal thing like a megaphone (panawag), a bell, or a horn. It can also be a name or a sound, like when you whistle for your dog, that's your panawag. Metaphorically, it's that "call to action" you see in ads, or the "call of duty" (panawagan ng tungkulin) you feel when your friend needs help moving out.