What is "inter-temporal smoothing"? In a recent article about the OECD latest report it reads as follows:


  Mr White said QE and easy money policies by the US Federal Reserve and
  its peers have had the effect of bringing spending forward from the
  future in what is known as "inter-temporal smoothing". It becomes a
  toxic addiction over time and ultimately loses traction. In the end,
  the future catches up with you. "By definition, this means you cannot
  spend the money tomorrow," he said.


What does he mean by "inter-temporal smoothing" and "bringing spending forward". How do you "bring spending forward"?
Intertemporal consumption smoothing is using savings or borrowing to make consumption less volatile than income (or sometimes wealth). The intertemporal consumption smoothing  motive can arise in many settings, but an early and famous example is the Milton Friedman’s permanent income hypothesis. The idea is that if income contains permanent and temporary shocks then maximizing the NPV of lifetime utility will make you ignore temporary shocks and consume a fixed fraction of your permanent income. 

Essentially, you know temporary shocks are temporary. If you cut back on consumption in the face of these temporary shocks you'd end up with consumption that is higher than average in better times. Because of declining marginal utility of consumption this is a worse consumption plan than keeping your consumption fixed in good times and bad. 

In contrast, if you experience a permanent negative shock to consumption there won't (in expectation) be a good time to make up for the lost income. Leaving your consumption unchanged in the present would therefore require even larger cutbacks in the future. This is a worse consumption plan than cutting your consumption immediately and using that new and lower plan going forward.