A pipeline config file can have one or more pipelines defined in it, but the definition of a single pipeline cannot be fragmented across multiple files. Pipeline config filenames can be any form you choose, although the convention for a single file is pipelines.yml.
Some things to note about pipelines:
You can have as many pipeline config files as you want. For example, our customers manage config in the following different ways:
Maintain a central DevOps repository and keep all pipeline config files for all projects in that repository.
Keep pipeline config files that build each microservice with the source code for that microservice.
Separating out pipeline steps and resources into separate config files (for example,
pipelines.steps.ymlandpipelines.resources.ymlrespectively).