Input/output operations per second is a function of a given amount of operations over time, in this case, seconds. This is a measurement of how many operations can be done over a second, and many applications provide a minimum requirement regarding IOPS.
Most applications provide a requirement of the minimum IOPS needed for it to work as expected. Make sure that these are met, as otherwise the application might not behave as intended.
When designing a storage solution, make sure IOPS is considered as a primary deciding factor when taking sizing decisions.