Tradecraft is a general term that denotes a skill acquired through experience in a (typically clandestine) trade.
The term is also used within the intelligence community as a collective word for the techniques used in modern espionage. It can be used to refer to general topics or techniques (dead drops, for example), or the specific techniques of a nation or organization (the particular form of encryption used by the NSA, for example).
The term in this sense is frequently used in the books of John le Carré and Tom Clancy, where characters frequently comment on others' tradecraft (including those of agents from the opposing side).