A cool, dark place, with top & neck of bottle utterly clean and re-sealed tight, to dissuade pests. Use it up fairly soon. Storing it in the fridge can cause crystallization, which you don’t want. Crystallized syrup can be rewarmed in its jar in a pan of water. Warm the water (under boiling temp) then turn off & let melt slowly. (Better to use it as a regular thing and get rid of all other sweeteners in the house.)