1. Please describe why this term needs to be added

What this term is about? (briefly)

• a kind of container that supports a primary app container

Why this term needs to be added? (briefly)

• regardless of how you orchestrate containers, the sidecar pattern is widely known and used

We shouldn't plagiarize https://learn.microsoft.com/en-us/azure/architecture/patterns/sidecar, but we can take inspiration from the way that Microsoft explain this topic.

2. Checklist

• The suggested term fits the cloud native definition or is essential to understanding cloud native terms. (We hope to avoid adding general or broad terminologies)
• There is no existing issue yet. (shift+click to check existing issues)
• The term has not already been declined in the past. (shift+click to check)
• The term does not already exist in the glossary as a completed term, nor does it exist in this directory as an incomplete term. (If the status of the term is Feedback Appreciated, consider updating the term.)
• I understand that maintainers will assess if the term should be part of the Glossary. (Please be patient)
• I want to work on this term and confirm that I meet the criteria as outlined in "who can contribute". (If not checked, maintainers will assign another volunteer)

(Note)

Maintainers will assign a label after assessment procedure.
(from triage/awaiting to triage/accepted or triage/not accepted)

A contributor can be assigned to this issue after the issue get the triage/accepted label.
The assignee needs to check Style Guide.