The term was popularised during the post-2010 period of aggressive monetary easing, when quantitative-easing in one economy after another was criticised by trading partners as devaluation by another name. The 1930s provide the historical template, when successive countries left the gold standard.
The logical problem is arithmetic: every currency cannot depreciate simultaneously, because each rate is a ratio. What actually results is a round of easier global policy, higher asset prices and a reshuffling of which currency is weakest this quarter.
Modern policy language avoids the topic carefully. Officials describe currency moves as a consequence of domestic policy rather than an objective, and G20 communiqués routinely include a commitment not to target exchange rates competitively.
Example: two central banks each cut 100 basis points in the same month. The interest-rate-differential between them is unchanged, so neither gets the depreciation it wanted, and both have looser domestic conditions.
Related: devaluation, quantitative-easing, central-bank-intervention, interest-rate-differential