Monetary inflation is simply an increase in the money supply. It is not measured by the Consumer Price Index but rather by the money supply. "Quantitative easing" is government speak for it. Inflating the money supply usually encourages spending and most government economists see increased spending as a way to keep the economy rolling. A currency that is defined in terms of a tangible substance (like gold or silver) is less likely to experience inflation. Although a rapid increase in supply of gold is possible, such as when Columbus opened up the importation of gold from the new world, it is extremely undesirable in the modern age.
"Monetary inflation" can result in price inflation, but the two terms are not synonymous. The most widely recognized effect of an increase in the money supply is a reduction of the value of each individual unit of money. As each unit decreases in value it results in the destruction of the purchasing power of your money. But while almost everyone sees price inflation when it happens, few people notice the monetary inflation that causes it.
Inflation of the US dollar supply has been an economic reality ever since 1913 when the US Congress created the Federal Reserve. This is because when the Federal Reserve buys US Treasuries it injects newly created money into the financial system. Another way of creating money out of thin air is through the fractional reserve system which allows banks to multiply the amount of money in circulation by only holding a fraction of what their actual liabilities are.
Central banks consider it the cure-all for combating all sorts of economic woes. If there is too much debt, just print more money, this allows the debtor to repay the debt with "cheaper dollars" ie dollars that are worth less than the original debt. This is a form of hidden theft from the creditor and benefits primarily the government as it is by far the nations largest debtor. Money creation is a debtor's greatest ally, making the debt easier to repay.
As the currency supply inflates, you would think, the price of all goods and services should appreciate proportionally, or at least roughly proportionally, as the value of the dollar decreases. But that is not always the case because the flow of money is not distributed evenly through the economy. Thus those who receive the money first get to spend it at the old perceived value while those at the bottom of the food chain receive the dollars later and suffer the most. Then once again, since the government created the new money it gets the most advantage, since it spends it first.
All monetary inflation is political andpetrated by the government (or more precisely the Central Bank). It is unsound for both economic and ethical reasons. All that newly created money has to go somewhere and it often flows toward the next bubble in the making. Monetary inflation is the seed inside all asset bubbles. Thus it wrecks the economy through booms and busts and creates disincentives for savers and creditors. It also causes misallocation of funds by businesses and individuals who perceive their income as growing when in actuality their real purchasing power may be staying the same or even declining. So it brings about wasteful and shortsighted economic decisions.