Noun

1. a conduit made of pipes used to convey water, gas or petroleum etc

   An oil pipeline has been opened from the Caspian Sea.

2. a channel (either physical or logical) by which information is transmitted sequentially (that is, the first information in is the first information out).

   3D images are rendered using the graphics pipeline.

3. a system through which something is conducted

   A new version of the software is in the pipeline, but has not been rolled-out.

4. : The inside of a wave that a surfer is riding, when wave has started closing over.

Verb

1. To convey something by a system of pipes
2. To lay a system of pipes through something