The action/s of an individual or a cohesive team to gather intelligence on unlawful or questionable activities of a chosen target (for or not) and by executing the reconnaissance mission unnoticed.
A combining of the words "secrecy" and "sneak". A way of moving in which you make less noise to avoid being caught, usually entailing creeping around very slowly.
Practicing sneakrecy will surely lead to much better scores in Call of Duty