You don't have to spend much time around cloud computing before you run into arguments regarding cloud economics and you will undoubtedly encounter the phrase "Capex vs. Opex." This refers to the fact that stocking your own data center requires capital expenditure, while using an external cloud service that offers pay-as-you-go service falls into ongoing operating expenditures: thus the contrast of "Capex vs. Opex." The next go-round of the argument then devolves into a tussle about which alternative is cheaper.
Source: CIO