Rosin

Rosin is the sap from pine tree. It is a sticky substance but can be processed and used for:

• Rosin is commonly used as a flux in metallurgy, especially for soldering.
• Bowss for musical instruments such as the violin are normally rubbed with rosin to increase the grip on the strings.
• It can also be used to demonstrate resonance in aluminium bars by stroking them with rosin tipped fingers.
• Ballet slippers are rubbed in powdered rosin to reduce slipping.
• Baseball pitchers use a rosin bag to keep their hands dry. Usage of rosin is specifically mentioned in major league baseball rules[1]
• Amateur telescope makers use a polishing lap made from rosin to polish and figure telescope mirrors and lenses.

Note that rosin is a specific type of resin. Not all resins are rosins.