What is Microlending?
Microlending is, in a nutshell, the lending of very small amounts.
Microlending and Microlending are both forms of Microfinance ;)
Personally, I don't restrict this to mean that the borrower is receiving a small amount, but the source of their loans is many parties.
1000 people lend $25 each to make for a $25000 loan. This is microlending, many people are lending a very small amount to make for a large loan. This makes a lot of sense, because it allows for someone with just a small amount of money, say $150, to loan to 6 different borrowers, thus diversifying their loan risk. This is the type of microlending offered by Prosper.com and, hopefully one day by Communitylend.
1 person lends $250 to one person for a $250 loan. This too is microlending, but more along the lines of microcredit, where the borrower is receiving a rather small amount of money, at least from our point-of-view. For those receiving the funds, however, this could actually amount to a great deal of money in purchasing power terms. This is along the lines of Kiva.org, although I believe many people can fund these loans as well.