1. Patchable permanent building runs, often connecting one room to another, or for ease of providing for location video or audio recording, i.e. video tielines, audio tielines.
2. Also known as trickline, #4 black cotton mason's cord. Primarily used to temporarily affix cable to a lighting position. When prepping the lighting equipment in a shop prior to loading into a venue, one often makes "pre-cuts": thirty or so parallel strands of 36" (two cubits) long tielines, tied in the center with a clove hitch.
(Management tends to get cranky when they see ten stagehands standing around watching one person cut tieline.)
Also found in the grommets of virtually every stage drape. Commonly purchased in spools of 250', 1000', or 3000', for around 3-4¢ per foot.
(Save time and money, re-use the tieline! Don't simply sweep it up and throw it away during load-out.)
NOTE: At least one member feels tieline and trickline are NOT interchangeable. He believes tie line to be the jute twine used to tie coils of cable (in the shop. It should be noted that this material is highly flammable and should NOT be used near hot fixtures. Shops use it because it is inexpensive. Most stagehands dislike it). Thus he feels the above entry should be "trick line" when referring to #4 black cotton mason's cord.