First, pipeline is not a bioinformatics term its actually a computer science term. It involves the chaining of processes/threads/functions etc. and the example John shows is an example of process threading. Commonly in bioinformatics we use Python (or another scripting language including UNIX shell) to create a pipeline in order to execute, then transform, then execute another program and so on. This chaining of programs allows a bioinformatician to start with one data type, say a FASTQ file obtained from next generation sequencing data (NGS) and end up with variant calling data. To do this a number of programs which analyze and translate the data must be executed.

If you’d like an example of a pipeline I’d recommending looking at GATK for a graphical representation of performing variant calling (SNPs & INDELs) take a look at

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Note added at 4 hrs (2017-08-24 20:40:20 GMT)
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https://www.quora.com/What-are-pipelines-in-Bioinformatics