What is this news
CPI (Consumer Price Index) measures changes in prices of everyday items: food, rent, fuel, clothes, services. This is the main inflation number. Released by National Statistics Institute (INE). This comes every month.
How important it is
The central bank's main job is to control inflation, so every interest rate decision is tied to this number. This is a High impact event on FxGram: EUR pairs often see sharp moves at this time.
What this data does
Generally, if inflation comes in above forecast, expectations of a rate hike (or rates staying high) increase, which affects the currency. If below forecast, talk of rate cuts increases.
This is just general knowledge (textbook), not a prediction for this release. The market may react differently. This is not buy-sell advice.