Goblining usually relates to video games (in particular first person shooters such as Call of Duty).
The act of goblining involves tucking yourself away in a corner, preferably under or behind native flora such as shrubs or tundra (man made objects such as overturned fridges can also be used) and lying in wait for an enemy to run past.
Goblining is a legitimate tactic and is used to defend objectives such as a capped flag in domination or a planted bomb in search and destroy. It should not be confused with camping, which is a similar tactic - however camping involves ignoring the objective completely.
Man the other day I was playing COD4 and I went in to defuse the bomb and this guy was prone in a nearby hay field underneath a tractor! That was some epic goblining skills right there..