"18 lohan hands" refers to the shih pa lo han sho which were supposedly the original 18 drills that Bodhidharma introduced to the Shaolin monks. As to who the "lohan" were, Bruce Haines describes them in his master's thesis (taken from Overlook's "Martial Arts Reader"):
"At the present time Lo-Han is used to designate all famous disciples of the historic Buddha, but more generally the term refers to those five hundred arhats (Sanskrit term for thos who achieved Nirvana) who are supposed to rappear on earth as Buddhas, according to Buddhist mythology in some sects of the religion.
The precise meaning of Lo-Han in Bodhidharma's time, however, is lost, and we are forced to rely on the educated assumption that they were some form of temple guardians of Hindu origin. It also appears that their original Hindu number was sixteen, and that the Chinese added two to bring the number to eighteen...
...For our purposes, however, the main significance of the shih pa lo han so, via Bodhidharma, is that it is reputed to be the basis for the famous Shaolin ch'uan fa."
In a similar way, ship pal gye, a Korean interpretation of Chinese Shaolin wushu, means 18 tenets or methods.