秘 is 'secret' or 'hidden'. 伝 is 'transmission'. This usually refers to hidden or so-called "secret" knowledge, knowledge that is not written down, not divulged to outsiders and is usually transmitted in an oral fashion only. This term specifically refers to special teachings or techniques (or the application and use of such techniques) within the context of a particular Japanese discipline, whether it be samisen playing, martial arts or ikebana. Most frequently I see it used when referring to various higher level martial arts techniques. Such techniques are usually only divulged after the disciple (whatever their discipline may be) has reach a certain (usually relatively advanced) level of proficiency within their chosen discipline. The typical method of transmission is directly from the teacher to the student and this can include both verbal instruction and, sometimes, demonstration of the actual techniques. This is the meaning of "hiden". HTH.