In a market economy the price of a product or asset can be expected to rise to reflect a rise in its underlying value. For example if a company develops a successful new product then the company has become more valuable, or if a new transport route opens near a property then the property has become more valuable. However another effect causes prices to rise over and above that expected from the underlying value change, but is often triggered by such a change, and that is when underlying value is expected to rise further, which causes new buyers to enter the market faster than new sellers. In these circumstances the price of the asset rises sharply as buyers try to get in before other buyers, and in the process bid prices up. This is an asset bubble, and it particularly affects property and shares.
What happens is that buyers are in a hurry to buy in order to obtain the asset as quickly as possible before other buyers can buy it, and bid the price up in order to persuade sellers to sell, but sellers, seeing this happen, become less inclined to sell because the asset is rising in value and delay is likely to result in a higher price. Hence the buyers' hurry to buy coupled with sellers' reluctance to sell creates a market that is rationed by supply, and a supply rationed market sees rising prices. In these circumstances the rationing is not for any reason other than the activities of buyers and sellers, and in that sense is induced by them.
The common belief is that more money is pouring into property or shares, so the price rises accordingly. That belief seems reasonable until it is recalled that money doesn't 'pour into' anything, it merely changes hands but always stays as money. For every purchase there is a sale, and as soon as money is used to buy an asset the seller immediately takes that money away. Therefore the price rise is not because of money pouring in, it is because of the rise in willingness to buy, coupled with a corresponding fall in willingness to sell, though the rise in willingness to buy is usually caused by a rise in the availability of money in the form of credit, especially for property.
The defining feature of an asset bubble is that buyers are buying not primarily because they want the immediate usefulness or the income that the asset promises to give them, but because the price is rising, and as a result they foresee further price rises that will net them a profit or save them from paying more in the future. This approach, which in the case of financial assets, is pure speculation, soon overwhelms any change in underlying value, and in the case of rising equity prices is known as the 'greater fool theory' - I may be a fool for paying such a silly price for this overpriced stock but there will be an even greater fool along shortly who will pay me even more than I paid for it. In the case of property bubbles a significant driver is the entry of investors into the market seeking both good returns from rents, which rise in accordance with prices, as well as capital gains. Induced rationing in the housing market is strongly assisted by real rationing due to new housing failing to keep pace with demand, creating an underlying supply rationed market, where even base-level prices put property out of reach of many would-be first-time buyers and also make rents too expensive for them.
The reverse happens when a bubble has run its course, and also happens without a bubble if there is an expectation of a future fall in value. In the case of a bubble, collapse is inevitable sooner or later, because there isn't an unlimited number of new buyers. As willing buyers obtain the assets they seek, their numbers drop and the price rise levels off. Seeing this the asset holders become more inclined to sell to avoid being left with an asset of falling value, and the willingness rapidly switches over. Now sellers are keener to sell than buyers to buy, and the price falls back again, often dramatically, not because the asset has changed in terms of its inherent value, but purely because sellers are desperate to offload and buyers are reluctant to buy into a falling market. Again rationing is induced by the activities of buyers and sellers, but this time the asset is rationed by demand.