Tubing is the pipe in the well up which the oil or gas flows to surface. A typical North Sea well design will have 7" tube (called casing) through the reservoir and then 4-1/2" or 5" tubing inside the casing, with a packer between the tubing and the casing just above the reservoir to isolate most of the 7" casing from the reservoir fluids.
To allow reservoir fluid from the rock into theh casing and then up the tubing, you need to blast holes in the casing with 'guns'- lots of small shaped charges. These gun strings can either be lowered into the well on the end of an armoured electrical wire or WIRELINE, or they can be attached to the tubing called TUBING CONVEYED PERFORATING(or TCP). TCP is quite popular as you can get bigger guns (wireline guns have to fit inside the tubing, unless you shoot, kill the well and then run the tubing, which takes time and often carries higher risk as the reservoir is open) and on horozontal or high angle wells, you can't lower guns on wireline, so you have to push them on the end of the tubing.
Wireline perforating in many areas is now only used for reperforating: blowing more holes or newer holes in the casing in an exisitng completion, to improve production or to access new producing zones.