Proof of Space uses hard disk space as the value used to guarantee a participant's stake in mining.
By allocating disk space, the network participant provides value to the network, which uses this space to solve computational problems.
Given low network bandwidth for a lot of regions, making it difficult to transfer large amounts of data to allocated hard drive space quickly, and considering the relatively inexpensive hard drive space, this system is not currently used on many mainstream cryptocurrencies.
BurstCoin uses the Proof of Space consensus algorithm.
See also: Proof of Capacity also uses Hard Drive space to solve cryptographic problems.
Return to main article: ELI5 Summary of cryptocurrency consensus mechanisms