What syrup do bartenders use?

As a curious individual interested in the intricacies of mixology, I'm wondering about the syrups that bartenders employ in their craft. Are there specific types of syrups tailored for various cocktails, or do they typically stick to a standard variety? I'm particularly intrigued by whether these syrups have unique flavors or if they serve more as a sweetening agent. Moreover, I'm curious about the preparation process for these syrups – are they homemade or sourced from specific suppliers? Lastly, I'm eager to learn about any trends or innovations in the syrups used by bartenders in recent times.