When I read this kind of question, or even read some articles on crypto's I always feel there's a big misunderstanding about the term "inflation".
In layman terms, the term inflation refers to purchasing power of a currency. Inflation actually measures the rate at which the price level moves over a given time horizon. If prices go up, then we say there’s inflation, if prices goes down, we say there is a deflation.
On a side note, it very difficult to measure all the prices in an economy, so the inflation measure observe a subset of prices, the price of a given basket of goods: the composition of such basket greatly influences the outcome of the inflation measure.
In the recent years, in the US and much more in the EU we have observed a decreasing inflation: prices have always been increasing but at a much lower pace. Every CB has a target of inflation, as a sole or conjunct target of around 2%. So broadly speaking we can think at this of a current level of inflation, while back in the 80’s we observed levels above 10%.
This means that the fiat currencies lose value in real terms: if I have to pay 2% every year to buy the same liter of milk of loaf of bread this doesn’t mean milk or bread increased value, but we are using a devalued currency: it’s like measuring your height with a shorter and shorter meter, you aren’t getting higher, you are using a shorter unit of measure.
What causes inflation is a very complex matter, some indication have been written here on the thread, but I will analyses only one of those: “money supply”.
Let’s think about an economy with stable inflation at 0%: prices are still, and I have been able to buy my milk for 1$ since 10 years. Let’s think about the CB governor going nut ant printing more money: he decided to print 1 additional dollar for every dollar available: everyone eventually get his extra dollar: what do you think it happen to prices? Yes, the same old liter of milk now it’s sold for 2 dollars.
Money supply is then the most important figure to look at to look at when trying to figure out where inflation is coming from.
Now to bitcoin.
Bitcoin is a deflationist currency: contrary to fiat currencies who have lost most of their values over the years (a gallon of milk cost 1.65$, while today is 4$) it has always been appreciating in real terms, this means it has always (not always actually if we think at December 2017) gained value. Two large pizzas were sold for 10,000 BTC in 2010, but now they are sold for 0.004 BTC.
In this sense bitcoin is a currency that has exhibited a deflation, even if the money supply has always been positive, yet decreasing.
Bitcoin money supply is predetermined, and halves every 210,000 blocks, typically every 4 years. Bitcoin money growth is the moment around 3,70%, and it will be halved to 1,80% at the next halving event.
To recap: bitcoin is currency with a money supply growing at decreasing rate. The market forces driving his price have caused Bitcoin to exhibit a deflationist behavior.
Money supply is hard coded in the bitcoin protocol, while the deflationist property is only the result of the balance between supply and demand on the market.
Regarding the relationship between halvin/monetary supply/price relationship the best advicee i can give you is read my thread in signature about SF model:
Stock To Flow Model: Modeling Bitcoin's Value with Scarcity