No, it's negative inflation! It is deflation only if you say so...

The International Monetary Fund defines deflation as a sustained fall in the general price level which occurs when the inflation rate falls below 0%. 

This will be applicable to you, unless you are the Bank of Thailand.

Consumer prices in Thailand fell last month for the first time since Sept. 2009. But the central bank says there is nothing to worry about - it is just negative inflation.

“The MPC viewed that negative inflation this time isn’t a signal of deflation,” Assistant Governor Mathee Supapongse said on Tuesday, because it’s temporary and caused by supply-side issues rather than from declining demand. The body sees "negative headline inflation" until the second quarter, and price gains in the first half of the year will be "mildly negative", he said.

According to Supapongse, the central bank, which began using headline inflation to guide monetary policy from January, expects it to turn positive from the third quarter, while the rate for the full year may be below an earlier forecast of 1.2%, reports Bloomberg. The negative rate of headline inflation at present "neither signals a deflationary environment nor constitutes risks to financial instability" because the decline in price levels isn't broad-based, and inflation expectations remain close to the target, while lower oil prices will boost domestic demand.

Mathee Supapongse

However, analysts seem less optimistic. After the data was released, ANZ published a note titled "Thailand: The return of deflation", and said there is a significant risk that the inflation rate will breach the lower end of the central bank's target of 1%.

Barclays estimates inflation is likely to remain negative for much of the first half, and lowered its 2015 average forecast to 0.2%.

While Thailand has not yet touched the spot of low wages and a broad-based fall in product prices, "risks of deflation are imminent," said Santitarn Sathirathai, Singapore-based economist for Southeast Asia at Credit Suisse Group AG. This year Credit Suisse has cut its inflation forecast to 0.6 percent from 2.2. percent, and said consensus estimates for average inflation are "still too high".

So, the Bank of Thailand should improve its convincing skills.