Best Answer: The easy answer is "it makes it go up". What you want to know is "how good a hedge against inflation is the stock market?"
In mainstream economics, the word “inflation” refers to a general rise in prices measured against a standard level of purchasing power. Previously the term was used to refer to an increase in the money supply, which is now referred to as expansionary monetary policy or monetary inflation. Inflation is measured by comparing two sets of goods at two points in time, and computing the increase in cost not reflected by an increase in quality. There are, therefore, many measures of inflation depending on the specific circumstances. The most well known are the CPI which measures consumer prices, and the GDP deflator, which measures inflation in the whole of the domestic economy.
The role of inflation in the economy
In the long run, inflation is generally believed to be a monetary phenomenon, while in the short and medium term, it is influenced by the relative elasticity of wages, prices and interest rates.  The question of whether the short-term effects last long enough to be important is the central topic of debate between monetarist and Keynesian schools. In monetarism, prices and wages adjust quickly enough to make other factors merely marginal behavior on a general trendline. In the Keynesian view, prices and wages adjust at different rates, and these differences have enough effects on real output to be "long term" in the view of people in an economy.
A great deal of economic literature concerns the question of what causes inflation and what effect it has. A small amount of inflation is often viewed as having a positive effect on the economy. One reason for this is that it is difficult to renegotiate some prices, and particularly wages, downwards, so that with generally increasing prices it is easier for relative prices to adjust. Many prices are "sticky downward" and tend to creep upward, so that efforts to attain a zero inflation rate (a constant price level) punish other sectors with falling prices, profits, and employment. Efforts to attain complete price stability can also lead to deflation, which is generally viewed as a negative outcome because of the significant downward adjustments in wages and output that are associated with it.
Inflation is also viewed as a hidden risk pressure that provides an incentive for those with savings to invest them, rather than have the purchasing power of those savings erode through inflation. In investing inflation risks often cause investors to take on more systematic risk, in order to gain returns that will stay ahead of expected inflation. Inflation is also used as an index for cost of living adjustments and as a peg for some bonds. In effect, inflation is the rate at which previous economic transactions are discounted economically.
Inflation also gives central banks room to maneuver, since their primary tool for controlling the money supply and velocity of money is by setting the lowest interest rate in an economy - the discount rate at which banks can borrow from the central bank. Since
borrowing at negative interest is generally ineffective, a positive inflation rate gives central bankers "ammunition", as it is sometimes called, to stimulate the economy.
However, in general, inflation rates above the nominal amounts required to give monetary freedom, and investing incentive, are regarded as negative, particularly because in current economic theory, inflation begets further inflationary expectations.
Increasing uncertainty may discourage investment and saving.
It will redistribute income from those on fixed incomes, such as pensioners, and shifts it to those who draw a variable income, for example from wages and profits which may keep pace with inflation.
Similarly it will redistribute wealth from those who lend a fixed amount of money to those who borrow. For example, where the government is a net debtor, as is usually the case, it will reduce this debt redistributing money towards the government. Thus inflation is sometimes viewed as similar to a hidden tax.
International trade: If the rate of inflation is higher than that abroad, a fixed exchange rate will be undermined through a weakening balance of trade.
Shoe leather costs: Because the value of cash is eroded by inflation, people will tend to hold less cash during times of inflation. This imposes real costs, for example in more frequent trips to the bank. (The term is a humorous reference to the cost of replacing shoe leather worn out when walking to the bank.)
Menu costs: Firms must change their prices more frequently, which imposes costs, for example with restaurants having to reprint menus.
Relative Price Distortions: Firms do not generally synchronize adjustment in prices. If there is higher inflation, firms that do not adjust their prices will have much lower prices relative to firms that do adjust them. This will distort economic decisions, since relative prices will not be reflecting relative scarcity of different goods.
Hyperinflation: if inflation gets totally out of control (in the upward direction), it can grossly interfere with the normal workings of the economy, hurting its ability to supply.
Inflation tax when a government can improve its net financial position by allowing inflation, then this represents a tax on certain holders of currency. Governments may decide to use this "stealth tax" in order to avoid hard fiscal decisions to cut expenditures, raise taxes, or confront government unions with greater efficiency.
Bracket Creep is related to the inflation tax. By allowing inflation to move upwards, certain sticky aspects of the tax code are met by more and more people. Commonly income tax brackets, where the next dollar of income is taxed at a higher rate than previous dollars. Governments that allow inflation to "bump" people over these thresholds are, in effect, allowing a tax increase because the same real purchasing power is being taxed at a higher rate.
As noted, some economists see moderate inflation as a benefit; some business executives see mild inflation as "greasing the wheels of commerce." A very few economists have advocated reducing inflation to zero as a monetary policy goal - particularly in the late 1990s at the end of a long disinflationary period, when the policy seemed within reach.