Clawhammer banjo is one particular style of banjo playing. Its historically a pure American form of "Old Time" music. It is called clawhammer because the hand that is used to strum and pick is held like a claw. A player does not roll like Scruggs style.
There is also a distinction between "clawhammer" and "frailing". While these styles can be interchangeable, the standard for frailing is to pick the drone string while in clawhammer, other strings are picked with the thumb (referred to as drop thumbing). There are other variations as well.
Frailing, Clawhammer and Old-Time music have been around since the birth of the banjo. It was Earl Scruggs, in the 60s who popularized the five string style that is played today.
None of these styles should be considered easier than the others. The all have their own characteristics that make the technique simple or more complicated to the student.
Hope this helps.