We get this question a lot and the fact is that manufactured homes are very different from modular homes. Many people get confused and use the two descriptions interchangeably, but there is an important difference between the two.
Modular homes are different from manufactured homes in that they are built according to regular building codes, the same ones that are applied to stick built homes. While modular homes are built in a factory, they are assembled at the building site and are as strong or stronger than regular houses. They are not outwardly different at all.
Manufactured homes, unlike modular homes, are regulated by different rules which require them to be constructed on a permanent chassis. Basically, manufactured homes are mobile homes. While still very useful and quite economical, manufactured homes are definitely different from modular homes.
Both these styles of houses are constructed in a factory, under controlled conditions, but a manufactured home is mobile, while a modular home is fixed.