If you are asking what is a 100% mortgage?   Basically, a mortgage is a secured long term loan for a property or home that you wish to purchase and the mortgage lender or bank, financial institution etc will lend you the money, based upon a mortgage repayment agreement of X amount of money for X amount of months.

The 100% means that you are asking the mortgage lender to finance the mortgage for the whole amount, therefore they are taking the whole risk on the property, in that if you should default on the repayments, and they then need to repossess the property, that they can reclaim the whole amount of the outstanding balance of the mortgage from the property.

If however you buy a property for 100% mortgages at 100k, and repay 2k, which leaves in theory 98k outstanding plus the interest added, the bank need to reclaim this figure.  If however in the meantime, the property market drops and the 100k property is now valued at 90k, then 2k has been repaid, and so 88k will be available in the actual building, yet 98k is outstanding, so there is a 10k negative equity plus the interest.

This scares the lenders in an uncertain market, when they are not sure which direction the market will go due to being in a recession, and the credit crunch, so they are nervous to lend 100 percent mortgages for this reason.