Meaning
A lightweight, standalone, executable package of software that includes everything needed to run an application: code, runtime, system tools, and libraries.
Three examples from work
Development environment
New hireHow do I spin up the backend and database locally?
MentorRun docker compose up; all services will launch inside isolated containers.
Deployment pipeline
DevOpsOur CI pipeline builds and tags a fresh Docker container on every merge to main.
DevThat guarantees that staging and production run identical binaries.
Resource limits
DevThe container crashed with an OOM killed error during batch image processing.
LeadIncrease the memory limit in the container specification to two gigabytes.
Popularized by Docker. Containers eliminate the classic 'it works on my machine' bug by packaging identical operating environments.