What does the arrow on the bottom left of the folder icon mean? As you see the mysql and mysql-5.7.17-macos10.12-x86_64 under the local path.
The mysql folder icon has a arrow on the bottom left.

Does the arrow mean shortcut to the mysql-5.7.17-macos10.12-x86_64? Or if not, if it is a other mysql entity folder?
The arrow means it is an alias or link, but it could lead anywhere. To find the destination, select the alias and press ⌘I (or right-click and choose Get Info), then look at the ‘Original’ path (or just open it and see where it leads).