The AMD Duron is mostly identical to its Athlon siblings. What differentiaties this CPU from the Athlon is its cache-- it has just 64k of L2 cache, whereas the Athlon has a full 256K. Like its more expensive counterpart, the Duron has a 128K L1 cache, but the L1 cache (that is, the data and instruction cache) of the Athlon is 16-way associative; the Duron's is only 2-way associative.
According to AMD, the name "Duron" is a combination of the Latin root "durare" (to last) and the suffix "-on," which means "unit".
There are two Duron cores: the Spitfire, which runs from 600MHz to 950MHz, and the Morgan, which includes Durons that are 1GHz and up, IIRC.