Vladimír Šimon, Pevnost, March 2017, www.signteach.eu
This podcast explains what classifiers are.
A classifier is a handshape that is associated with a particular meaning. For instance, the 1-handshape can refer to long, thin objects, the 3-handshape to vehicles.
Classifier handshapes can be used to modify the 'library' form of signs, to indicate a more specific meaning. For instance, when you sign GIVE, you can use a classifier to specify what you are giving: something small or big, flat or round, light or heavy.