Yes, voluntary savings are financial assets that are put aside for future use. However, we must note that not all assets that we put away for future use are voluntary savings.
The term "voluntary savings" is typically used in the context of microfinance. It is distinguished from compulsory savings. Compulsory savings are those savings that must be put aside as a condition of getting a loan. By contrast, a saver is not required to put away any voluntary savings. These assets are put away by the saver for later use purely because the saver believes it is advisable to do so.
Not all assets put away for future use are voluntary savings, but voluntary savings are assets that are put away for future use.