Synaptics is a company that makes human interface devices like touchpads. Synaptic is a Linux package manager that works with Apt. At some point in the past, these two tags were incorrectly synonomized.
synaptics is a manufacturer tag and should be added to the list for tag cleanup after any questions about the package manager have been separated and retagged.
If the two tags were merged as well as synonomized, the cleanup will be more complicated. There are 158 questions with the synonomized tag. It looks like about 35 of those relate to package management. A search for questions with both "synaptic" and "package" text found 99, while "synaptic" incorrectly paired with "touchpad" found 233. So if necessary, questions could be retagged with a new synaptics-touchpad tag, or the existing generic touchpad, after which retagging the package management questions with synaptic or synaptic-pkg-mgr wouldn't be a massive task. If the more unique synaptic-pkg-mgr tag is created, it will be easy to retag the package management questions first, then cleanup the touchpad questions.